Streamline test suite and CI workflows

[Widthdom]

Summary

• Consolidate redundant test fixtures and assertions across language, database, archive, Git, JSON, and reference-extractor coverage.
• Reduce repeated setup and retained output in test workflows, while reusing build artifacts and scoping caches and artifacts to the inputs they validate.
• Apply the same reductions across C#, JVM, SQL, Python, Rust, Swift, COBOL, and Shell coverage.
• Keep bilingual testing and workflow contract documentation aligned with the optimized behavior.
• Synchronize the README status contract fields required by CI, including FTS maintenance counters and MCP metrics queue/failure/recovery diagnostics.

Validation

• .NET 8 Release full suite before the CI follow-up: 11,012 tests, 11,004 passed, 7 skipped, with the README status contract as the remaining failure; 22m39s observed.
• .NET 9 Release full suite before the CI follow-up: 10,951 tests, 10,545 passed, 405 skipped, with the same README status contract as the remaining failure; 21m34s observed.
• The repaired DocumentationStatusContractTests pass for both .NET 8 and .NET 9 (3/3 each).
• Baseline .NET 8 duration was 34m54s, an observed reduction of about 35%.
• Debug builds completed after every commit, including the CI follow-up, with zero warnings and errors.
• dotnet format CodeIndex.sln --verify-no-changes --no-restore passed.
• Independent adversarial reviews for test contracts and CI/workflows completed with no findings after follow-up fixes.

The branch contains 22 coherent commits and tracks origin/test/streamline-suite-and-ci.