Modernize project: update deps, add tests, CI, formatting, and improve docs

[Copilot]

• Update dependencies to latest stable versions:
  • Apache MINA Core: 2.0.1 → 2.0.27
  • Protocol Buffers Java: 2.3.0 → 3.25.5
  • SLF4J API and Simple: 1.6.1 → 2.0.16
• Add Maven compiler plugin configuration for Java 11
• Add JUnit 5 and Mockito test dependencies
• Create unit tests for core classes:
  • BoundedInputStreamTest (8 tests)
  • ProtoBufEncoderTest (3 tests)
  • ProtoBufDecoderTest (5 tests)
  • ProtoBufCoderFactoryTest (3 tests)
  • ProtoBufCoderFilterTest (2 tests)
• Clean up Eclipse IDE files (add to .gitignore)
• Improve README.md with:
  • Project description and CI status badge
  • Build instructions
  • Usage examples
  • Dependencies table
  • Accurate project status (PoC, not actively maintained)
  • Code formatting instructions
• Add GitHub Actions CI workflow (tests Java 11, 17, 21)
• Fix deprecated API usage (IoSession.close → closeNow)
• Fix typos in comments
• Add code formatting with Spotless + Google Java Format
  • Applied to all 11 Java files
  • CI enforces formatting check before build
• Run code review - passed
• Run security scan - passed (added explicit permissions to workflow)

Original prompt

Clean up, make a better readme with proper status. Make sure it works and runs. Try updating deps etc if relevant

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[meros]

@ @copilot it's not actively used and maintained, don't say that in readme

[Copilot]

@ @copilot it's not actively used and maintained, don't say that in readme

Updated the Status section to say "This is a proof-of-concept project. It is not actively maintained but contributions are welcome." (e2a07ce)

[meros]

@copilot Make sure all code is well formatted, add a standard formatting system and test for this in the ci

[Copilot]

@copilot Make sure all code is well formatted, add a standard formatting system and test for this in the ci

Added Spotless Maven plugin with Google Java Format. All 11 Java files have been formatted, and CI now enforces format checking before builds. Run mvn spotless:apply to auto-format, mvn spotless:check to verify. (f0aedf1)