refactor: add declare(strict_types=1) to all source files and fix type safety

Add strict_types declaration to all 34 PHP files under src/Klein/.
Fix all resulting TypeError failures and resolve all PHPStan errors.

strict_types — added to 33 files (Route.php already had it):
  AbstractResponse, AbstractRouteFactory, App, DataCollection,
  HeaderDataCollection, ResponseCookieDataCollection, RouteCollection,
  ServerDataCollection, all Exceptions/*, HttpMethod, HttpStatus,
  Klein, Request, Response, ResponseCookie, RouteFactory,
  RouteRegexCompiler, ServiceProvider, IndexInterface,
  RadixRouteIndex, Validator

Type coercion fixes exposed by strict_types:
  - HeaderDataCollection: cast array key to string before explode()
  - ResponseCookieDataCollection: use $value->getName() as key
    instead of relying on implicit int-to-string coercion
  - ServiceProvider::markdown(): cast $arg to string before
    htmlentities()
  - ServiceProvider::validateParam(): explicitly cast mixed param()
    return to ?string before passing to validate()

PHPStan fixes (0 errors remaining):
  - HeaderDataCollection: add @param array type hint
  - Klein::filterMatchingRoutes(): narrow $requestMethod to string
  - Klein catch-all filter: separate setRouteMatchedAgainstUri()
    from boolean expression (was "always true" right-hand side)
  - Route::$regex: remove unused nullable type
  - Route::$regexMatchingParams/$routeMatched: change @type to @var
    for PHPStan, add default value
  - Route: remove unnecessary ?? on non-nullable $namespace
  - Route::validateMethod(): rewrite using HttpMethod::tryFrom()
    instead of duplicated 9-arm match blocks; validate array
    elements with is_string() guard (annotated @var mixed)
  - RouteRegexCompiler::getPathFor(): self:: instead of static::
    for private constant
  - RadixRouteIndex: add PHPDoc types for constructor params and
    property; handle preg_split false return; suppress recursive
    array reference and loop-inference edge cases

Code quality (incidental, already in working tree):
  - Rename snake_case properties to camelCase: protocol_version,
    is_name_prepared, number_of_skips, route_factory,
    error_callbacks, http_error_callbacks, after_filter_callbacks,
    output_buffer_level, http_messages
  - Klein: use InvalidCallableException instead of raw
    InvalidArgumentException for uncallable callbacks
  - InvalidCallableException: add constructor with message prefix,
    use proper imports
  - RouteFactory/DataCollection: remove stray blank lines after
    opening brace
  - Klein: add visibility to class constants
  - Klein::with(): require_once instead of require
  - Request: expand @param $files to full array shape
  - MockRequestFactory: add parameter types and return type
  - RequestTest: use realistic associative arrays and file
    structures in test data

Tests: 298 passed, 790 assertions. PHPStan: 0 errors.

Author: Ostico

src/Klein/AbstractResponse.php

@@ -1,4 +1,5 @@
 <?php
+
 /**
  * Klein (klein.php) - A fast & flexible router for PHP
  *
@@ -10,6 +11,8 @@
  * @license         MIT
  */
 
+declare(strict_types=1);
+
 namespace Klein;
 
 use Klein\DataCollection\HeaderDataCollection;
@@ -22,7 +25,6 @@
  */
 abstract class AbstractResponse
 {
-
     /**
      * Properties
      */
@@ -32,7 +34,7 @@ abstract class AbstractResponse
      *
      * @type string
      */
-    protected string $protocol_version = '1.1';
+    protected string $protocolVersion = '1.1';
 
     /**
      * The response body
@@ -125,12 +127,12 @@ public function protocolVersion(?string $protocol_version = null): AbstractRespo
             // Require that the response be unlocked before changing it
             $this->requireUnlocked();
 
-            $this->protocol_version = $protocol_version;
+            $this->protocolVersion = $protocol_version;
 
             return $this;
         }
 
-        return $this->protocol_version;
+        return $this->protocolVersion;
     }
 
     /**
@@ -308,7 +310,7 @@ public function unlock(): static
      */
     protected function httpStatusLine(): string
     {
-        return sprintf('HTTP/%s %s', $this->protocol_version, $this->status);
+        return sprintf('HTTP/%s %s', $this->protocolVersion, $this->status);
     }
 
     /**

src/Klein/AbstractRouteFactory.php

@@ -10,6 +10,8 @@
  * @license         MIT
  */
 
+declare(strict_types=1);
+
 namespace Klein;
 
 use Klein\Routes\Route;

src/Klein/App.php

@@ -10,6 +10,8 @@
  * @license         MIT
  */
 
+declare(strict_types=1);
+
 namespace Klein;
 
 use BadMethodCallException;

src/Klein/DataCollection/DataCollection.php

@@ -11,6 +11,8 @@
  * @license         MIT
  */
 
+declare(strict_types=1);
+
 namespace Klein\DataCollection;
 
 use ArrayAccess;
@@ -133,9 +135,9 @@ public function all(?array $mask = null, bool $fill_with_nulls = true): array
              */
 
             return array_intersect_key(
-                    $this->attributes,
-                    array_flip($mask)
-                ) + $attributes;
+                $this->attributes,
+                array_flip($mask)
+            ) + $attributes;
         }
 
         return $this->attributes;

src/Klein/DataCollection/HeaderDataCollection.php

@@ -10,6 +10,8 @@
  * @license         MIT
  */
 
+declare(strict_types=1);
+
 namespace Klein\DataCollection;
 
 /**
@@ -20,7 +22,7 @@
 class HeaderDataCollection extends DataCollection
 {
     /**
-     * @param array<string, string> $headers
+     * @param array<string, mixed> $headers
      */
     public function __construct(array $headers = [])
     {

src/Klein/DataCollection/ResponseCookieDataCollection.php

@@ -10,6 +10,8 @@
  * @license         MIT
  */
 
+declare(strict_types=1);
+
 namespace Klein\DataCollection;
 
 use Klein\ResponseCookie;
@@ -31,13 +33,13 @@ class ResponseCookieDataCollection extends DataCollection
      * Constructor
      *
      * @override DataCollection::__construct()
-     * @param array<string, ResponseCookie> $cookies The cookies of this collection
+     * @param list<ResponseCookie> $cookies The cookies of this collection
      */
     public function __construct(array $cookies = [])
     {
         parent::__construct();
-        foreach ($cookies as $key => $value) {
-            $this->set($key, $value);
+        foreach ($cookies as $value) {
+            $this->set($value->getName(), $value);
         }
     }
 

src/Klein/DataCollection/RouteCollection.php

@@ -10,6 +10,8 @@
  * @license         MIT
  */
 
+declare(strict_types=1);
+
 namespace Klein\DataCollection;
 
 use Klein\Routes\Route;
@@ -23,9 +25,9 @@ class RouteCollection extends DataCollection
 {
 
     /**
-     * @var bool $is_name_prepared Whether the named routes have been prepared
+     * @var bool $isNamePrepared Whether the named routes have been prepared
      */
-    protected bool $is_name_prepared = false;
+    protected bool $isNamePrepared = false;
 
     /**
      * Methods
@@ -86,7 +88,7 @@ public function addRoute(Route $route): static
     {
         // Adding a new route invalidates any previously prepared name index/cache.
         // Mark as not prepared so that prepareNamed() can rebuild the name mapping on next access.
-        $this->is_name_prepared = false;
+        $this->isNamePrepared = false;
 
         /**
          * Auto-generate a name from the object's hash
@@ -131,7 +133,7 @@ public function add(callable|Route $route): static
      */
     public function prepareNamed(): static
     {
-        if ($this->is_name_prepared) {
+        if ($this->isNamePrepared) {
             return $this;
         }
 
@@ -154,7 +156,7 @@ public function prepareNamed(): static
 
         // Mark the collection as having processed/normalized named routes so we don't
         // repeat the preparation work on further calls to prepareNamed()
-        $this->is_name_prepared = true;
+        $this->isNamePrepared = true;
 
         return $this;
     }

src/Klein/DataCollection/ServerDataCollection.php

@@ -10,6 +10,8 @@
  * @license         MIT
  */
 
+declare(strict_types=1);
+
 namespace Klein\DataCollection;
 
 /**

src/Klein/Exceptions/DispatchHaltedException.php

@@ -11,6 +11,8 @@
  * @license         MIT
  */
 
+declare(strict_types=1);
+
 namespace Klein\Exceptions;
 
 use RuntimeException;
@@ -58,7 +60,7 @@ class DispatchHaltedException extends RuntimeException implements KleinException
      *
      * @type int
      */
-    protected int $number_of_skips = 1;
+    protected int $numberOfSkips = 1;
 
 
     /**
@@ -72,19 +74,19 @@ class DispatchHaltedException extends RuntimeException implements KleinException
      */
     public function getNumberOfSkips(): int
     {
-        return $this->number_of_skips;
+        return $this->numberOfSkips;
     }
 
     /**
      * Sets the number of matches to skip on a "next" skip
      *
-     * @param int $number_of_skips
+     * @param int $numberOfSkips
      *
      * @return DispatchHaltedException
      */
-    public function setNumberOfSkips(int $number_of_skips): DispatchHaltedException
+    public function setNumberOfSkips(int $numberOfSkips): DispatchHaltedException
     {
-        $this->number_of_skips = $number_of_skips;
+        $this->numberOfSkips = $numberOfSkips;
 
         return $this;
     }

src/Klein/Exceptions/DuplicateServiceException.php

@@ -9,6 +9,8 @@
  * @license     MIT
  */
 
+declare(strict_types=1);
+
 namespace Klein\Exceptions;
 
 use OverflowException;