refactor: split container tests into per-component test files

- Extract Tomcat tests to tomcat_test.go
- Extract Spring Boot tests to spring_boot_test.go
- Extract Groovy tests to groovy_test.go
- Extract Java Main tests to java_main_test.go
- Extract Dist ZIP tests to dist_zip_test.go
- Reduce container_test.go to Registry tests only (874 → 128 lines)
- Improve maintainability and align with project conventions
- All 83 tests pass with no regressions

Author: ramonskie