Add org.cactoos.map.Immutable decorator and related docs/tests

Introduce a read-only Map decorator consistent with list/set Immutable
classes, document usage in the README (including SplitPreserveAllTokens
examples for the existing text API), and add unit tests for map.Immutable
and TriFuncSplitPreserve.

Keep the Maven CI matrix on ubuntu-24.04, windows-2022, and macos-15.
Pass -Dhone.skipWithoutDocker=true so hone runs when Docker is present
(Ubuntu) and is skipped cleanly on runners without Docker.

Closes #1835

Author: rehandxtr

.github/workflows/mvn.yml

@@ -15,6 +15,7 @@ jobs:
     timeout-minutes: 15
     runs-on: ${{ matrix.os }}
     strategy:
+      fail-fast: false
       matrix:
         os: [ubuntu-24.04, windows-2022, macos-15]
         java: [23]
@@ -32,4 +33,5 @@ jobs:
             ${{ runner.os }}-jdk-${{ matrix.java }}-maven-
       - run: java -version
       - run: mvn -version
-      - run: mvn --errors --batch-mode clean install -Pqulice
+      # hone-maven-plugin needs Docker; skip it when Docker is unavailable (macOS/Windows runners).
+      - run: mvn --errors --batch-mode clean install -Pqulice -Dhone.skipWithoutDocker=true

README.md

@@ -110,6 +110,63 @@ new Upper(
 );
 ```
 
+### Splitting Text
+
+To split text using Java's standard behavior:
+
+```java
+Iterable<Text> parts = new Split("hello,world", ",");
+// Result: ["hello", "world"]
+```
+
+### Splitting with Preserved Empty Tokens
+
+Java's `String.split()` discards trailing empty tokens.
+Use `SplitPreserveAllTokens` when you need to preserve ALL tokens,
+including empty ones created by adjacent or trailing delimiters:
+
+```java
+// Standard split loses trailing empty token
+"a,b,".split(",")  // Returns: ["a", "b"] - trailing empty LOST!
+
+// SplitPreserveAllTokens preserves it
+Iterable<Text> parts = new SplitPreserveAllTokens("a,b,", ",");
+// Result: ["a", "b", ""]  - all tokens preserved!
+```
+
+This is essential for parsing CSV/TSV data where empty fields are meaningful:
+
+```java
+// Parse CSV with empty fields
+Iterable<Text> fields = new SplitPreserveAllTokens(
+  "John,,Smith,,"
+  ","
+);
+// Result: ["John", "", "Smith", "", ""]  - all 5 fields!
+
+// With spaces as delimiter
+Iterable<Text> words = new SplitPreserveAllTokens(" hello  world ");
+// Result: ["", "hello", "", "world", ""]
+
+// Default delimiter is space
+Iterable<Text> tokens = new SplitPreserveAllTokens("a b c");
+// Result: ["a", "b", "c"]
+
+// With limit on number of tokens
+Iterable<Text> limited = new SplitPreserveAllTokens("a,b,c,d", ",", 2);
+// Result: ["a", "b"]
+```
+
+**Key guarantee**: With N delimiters, you always get exactly N+1 tokens.
+
+| Input | Delimiter | `String.split()` | `SplitPreserveAllTokens` |
+| ------- | ----------- | ------------------ | -------------------------- |
+| `"a,b,"` | `,` | `["a", "b"]` | `["a", "b", ""]` |
+| `",,"` | `,` | `[]` | `["", "", ""]` |
+| `","` | `,` | `[]` | `["", ""]` |
+
+> **Note**: The delimiter is matched as a literal string, not a regex.
+
 ## Iterables/Collections/Lists/Sets
 
 More about it here:
@@ -254,6 +311,54 @@ final Set<String> sorted = new org.cactoos.set.Sorted<>(
 );
 ```
 
+## Maps
+
+To create a simple map:
+
+```java
+Map<String, Integer> map = new MapOf<>(
+  new MapEntry<>("one", 1),
+  new MapEntry<>("two", 2),
+  new MapEntry<>("three", 3)
+);
+```
+
+### Immutable Maps
+
+To create an immutable (read-only) map that prevents any modifications:
+
+```java
+Map<String, Integer> map = new org.cactoos.map.Immutable<>(
+  new MapOf<>(
+    new MapEntry<>("one", 1),
+    new MapEntry<>("two", 2)
+  )
+);
+map.get("one");      // returns 1
+map.put("three", 3); // throws UnsupportedOperationException!
+map.clear();         // throws UnsupportedOperationException!
+```
+
+The `Immutable` map decorator guarantees that:
+
+- Mutating methods (`put`, `remove`, `putAll`, `clear`) are blocked
+- Views from `keySet()`, `values()`, and `entrySet()` are immutable
+- `Entry.setValue()` is blocked on entries from `entrySet()`
+
+This is useful when you need to pass a map to untrusted code or ensure
+a map cannot be accidentally modified:
+
+```java
+// Safe to pass to any method - cannot be modified
+public Map<String, Config> getConfiguration() {
+  return new Immutable<>(this.config);
+}
+```
+
+> **Note**: This is a decorator, not a copy. If the underlying map is modified
+> through another reference, changes will be visible. For a true snapshot,
+> copy the data first.
+
 ## Funcs and Procs
 
 This is a traditional `foreach` loop:
@@ -331,6 +436,7 @@ final String text = new TextOfDateTime(date).asString();
 | `And` | `Iterables.all()` | - | - |
 | `Filtered` | `Iterables.filter()` | ? | - |
 | `FormattedText` | - | - | `String.format()` |
+| `map.Immutable` | `ImmutableMap` | `UnmodifiableMap` | `unmodifiableMap()` |
 | `IsBlank` | - | `StringUtils.isBlank()` | - |
 | `Joined` | - | - | `String.join()` |
 | `LengthOf` | - | - | `String#length()` |
@@ -342,6 +448,7 @@ final String text = new TextOfDateTime(date).asString();
 | `Reversed` | - | - | `StringBuilder#reverse()` |
 | `Rotated` | - | `StringUtils.rotate()` | - |
 | `Split` | - | - | `String#split()` |
+| `SplitPreserveAllTokens` | - | `StringUtils.splitPreserveAllTokens()` | - |
 | `StickyList` | `Lists.newArrayList()` | ? | `Arrays.asList()` |
 | `Sub` | - | - | `String#substring()` |
 | `SwappedCase` | - | `StringUtils.swapCase()` | - |
@@ -449,26 +556,26 @@ in GitHub precommits.
 
 ## Contributors
 
-* [@yegor256](https://github.com/yegor256) as Yegor Bugayenko ([Blog](http://www.yegor256.com))
-* [@g4s8](https://github.com/g4s8) as [Kirill Che.](mailto:g4s8.public@gmail.com)
-* [@fabriciofx](https://github.com/fabriciofx) as Fabrício Cabral
-* [@englishman](https://github.com/englishman) as Andriy Kryvtsun
-* [@VsSekorin](https://github.com/VsSekorin) as Vseslav Sekorin
-* [@DronMDF](https://github.com/DronMDF) as Andrey Valyaev
-* [@dusan-rychnovsky](https://github.com/dusan-rychnovsky) as Dušan Rychnovský ([Blog](http://blog.dusanrychnovsky.cz/))
-* [@timmeey](https://github.com/timmeey) as Tim Hinkes ([Blog](https://blog.timmeey.de))
-* [@alex-semenyuk](https://github.com/alex-semenyuk) as Alexey Semenyuk
-* [@smallcreep](https://github.com/smallcreep) as Ilia Rogozhin
-* [@memoyil](https://github.com/memoyil) as Mehmet Yildirim
-* [@llorllale](https://github.com/llorllale) as George Aristy
-* [@driver733](https://github.com/driver733) as Mikhail Yakushin
-* [@izrik](https://github.com/izrik) as Richard Sartor
-* [@Vatavuk](https://github.com/Vatavuk) as Vedran Grgo Vatavuk
-* [@dgroup](https://github.com/dgroup) as Yurii Dubinka
-* [@iakunin](https://github.com/iakunin) as Maksim Iakunin
-* [@fanifieiev](https://github.com/fanifieiev) as Fevzi Anifieiev
-* [@victornoel](https://github.com/victornoel) as Victor Noël
-* [@paulodamaso](https://github.com/paulodamaso) as Paulo Lobo
+- [@yegor256](https://github.com/yegor256) as Yegor Bugayenko ([Blog](http://www.yegor256.com))
+- [@g4s8](https://github.com/g4s8) as [Kirill Che.](mailto:g4s8.public@gmail.com)
+- [@fabriciofx](https://github.com/fabriciofx) as Fabrício Cabral
+- [@englishman](https://github.com/englishman) as Andriy Kryvtsun
+- [@VsSekorin](https://github.com/VsSekorin) as Vseslav Sekorin
+- [@DronMDF](https://github.com/DronMDF) as Andrey Valyaev
+- [@dusan-rychnovsky](https://github.com/dusan-rychnovsky) as Dušan Rychnovský ([Blog](http://blog.dusanrychnovsky.cz/))
+- [@timmeey](https://github.com/timmeey) as Tim Hinkes ([Blog](https://blog.timmeey.de))
+- [@alex-semenyuk](https://github.com/alex-semenyuk) as Alexey Semenyuk
+- [@smallcreep](https://github.com/smallcreep) as Ilia Rogozhin
+- [@memoyil](https://github.com/memoyil) as Mehmet Yildirim
+- [@llorllale](https://github.com/llorllale) as George Aristy
+- [@driver733](https://github.com/driver733) as Mikhail Yakushin
+- [@izrik](https://github.com/izrik) as Richard Sartor
+- [@Vatavuk](https://github.com/Vatavuk) as Vedran Grgo Vatavuk
+- [@dgroup](https://github.com/dgroup) as Yurii Dubinka
+- [@iakunin](https://github.com/iakunin) as Maksim Iakunin
+- [@fanifieiev](https://github.com/fanifieiev) as Fevzi Anifieiev
+- [@victornoel](https://github.com/victornoel) as Victor Noël
+- [@paulodamaso](https://github.com/paulodamaso) as Paulo Lobo
 
 [blog]: http://www.yegor256.com/2017/06/22/object-oriented-input-output-in-cactoos.html
 [OffsetDateTime]: https://docs.oracle.com/javase/8/docs/api/java/time/OffsetDateTime.html