Migrate to Java 25

[Copilot]

Upgrades the project from Java 11 to Java 25, modernising both the build configuration and source code to use current Java features.

Build

• maven.compiler.release → 25; removed redundant maven.compiler.source
• maven-compiler-plugin 3.11.0 → 3.15.0
• maven-surefire-plugin / maven-failsafe-plugin 3.2.2 → 3.5.5
• Added --add-opens JVM args for Java 25 module system compatibility (Mockito/byte-buddy)
• CI: JDK 11 → 25

Source modernisation

• Instance main method (finalized in Java 25):

  // before
  public static void main(String[] args) throws Exception { ... }
  // after
  void main(String[] args) throws Exception { ... }

• Unnamed catch variables (_) for unused exceptions
• Pattern-matching instanceof replacing explicit casts
• Switch expressions replacing traditional switch statements
• "%02x".formatted(b) replacing String.format("%02x", b)