Major changes:
Run 4 build configurations in parallel with Valgrind on Linux
Add test failure detection verification (meta-test)
Port allocation per build to prevent conflicts in parallel runs
Add --coverage-only flag for dedicated coverage builds
Code quality:
Add TEST_GROUPS constant, CMOCKA patterns, helper functions
Organize ci-build.sh into sections
Split functional tests into 4 parallel groups and add check-functional-parallel target (~3x faster CI runs).
Add branch-aware LCOV coverage reporting with new --enable-coverage option and lcov summary in CI pipeline.
Enable ccache via -C configure flag for faster recompilations.
Install lcov in all Docker images and use --depth 1 git clones + parallel make -j$(nproc) for quicker container builds.
Update CONTRIBUTING.md with instructions for parallel test groups and adding new ones.
All changes are tightly related CI/performance improvements developed in sequence. No external service uploads (e.g. Codecov skipped due to Gitea incompatibility).
