Adding tests and GH Actions CI

[cergfix]

Summary

Add CI/CD pipeline, comprehensive test suite (97 tests, 91% line coverage), and Checkstyle linting. Replaces the defunct Travis CI config and manual integration test. Documents 3 known bugs in FCGIConnection scatter read / STDERR handling with failing tests.

Changes

• Upgraded from JUnit 3.8.1 to JUnit 5 (5.10.2) in pom.xml, added maven-compiler-plugin, maven-surefire-plugin, JaCoCo, and Checkstyle
• Deleted .travis.yml and manual Test.java integration test
• Added GitHub Actions CI (.github/workflows/ci.yml): Checkstyle on Java 17, test matrix on Java 8/11/17/25
• Added checkstyle.xml with practical rules (imports, naming, coding patterns, brace style)
• Added PR template (.github/pull_request_template.md)
• Added 97 unit/integration tests across 11 test files:
• Enum constants (FCGIHeaderType, FCGIProtocolStatus, FCGIRole)
• Messages (FCGIHeader, FCGIBeginRequest, FCGIEndRequest, FCGIParams, FCGIStdin)
• Utilities (IoUtils) and exceptions (FCGIException)
• FCGIConnectionTest with mock FCGI server: issue Truncated responses #6 regression (truncated responses), issue php5-fpm: Connection reset by peer (read) #7 regression (STDERR handling), write path, error guards, exception paths
• Documented 3 known bugs in README with links to source lines and failing tests:
  • Scatter read doesn't handle STDERR frames
  • STDERR-first breaks response header parsing
  • Scatter read drops non-STDOUT frames without consuming body

Test plan

• mvn verify passes locally (94 pass, 3 expected failures for known bugs)
• mvn checkstyle:check passes with 0 violations
• Known bug tests verified to fail correctly
• CI runs on GitHub Actions after push

[cergfix]

Fixes #11