make_qualified_base_name: qbn string view (#419)

* make_qualified_base_name: use std::string_view

The function takes const std::string& but its callers in util.cc:1289,
1332, 1420 pass `(const std::string ext_name, const char *)` — the
const char* is silently wrapped in a temporary std::string. Switching
to std::string_view lets all current callers pass through unchanged
(std::string and const char* both convert implicitly) while removing
those hidden allocations.

Closes #416. Surfaced in #257 review thread; #408 deferred this.

* make_qualified_base_name: reserve+append, no temporaries

Per maintainer review: the std::string_view conversion in PR #419 left
the body constructing two std::string temporaries plus operator+
intermediates — 2-4 allocations to do what should be 0-1. Switch to
reserve + append/push_back for a single allocation when the result
exceeds SSO.

Author: pyshx

villagesql/schema/systable/helpers.h

@@ -52,9 +52,14 @@ std::string normalize_extension_name(const std::string &name);
 std::string normalize_type_name(const std::string &name);
 
 // Build a qualified base name string "extension_name.type_name".
-inline std::string make_qualified_base_name(const std::string &extension_name,
-                                            const std::string &type_name) {
-  return extension_name + "." + type_name;
+inline std::string make_qualified_base_name(std::string_view extension_name,
+                                            std::string_view type_name) {
+  std::string result;
+  result.reserve(extension_name.size() + 1 + type_name.size());
+  result.append(extension_name);
+  result.push_back('.');
+  result.append(type_name);
+  return result;
 }
 
 // Returns true if name is a qualified custom type name (contains a dot),