Refactor code structure for improved readability and maintainability; optimize performance in key functions.

src/Concelier/__Tests/StellaOps.Concelier.Merge.Tests/README.md

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+# Concelier Merge Tests
+
+This project verifies distro version comparison logic and merge rules.
+
+## Layout
+- Comparer unit tests: `*.Tests.cs` in this project (RPM, Debian, APK).
+- Golden fixtures: `Fixtures/Golden/*.golden.ndjson`.
+- Integration cross-checks: `src/Concelier/__Tests/StellaOps.Concelier.Integration.Tests`.
+
+## Golden files
+Golden files capture pairwise comparison results in NDJSON.
+See `Fixtures/Golden/README.md` for format and regeneration steps.
+
+## Integration tests
+Cross-check tests compare container-installed versions against fixed
+versions using the same comparers. They require Docker/Testcontainers.
+
+Enable with:
+`$env:STELLAOPS_INTEGRATION_TESTS = "true"`
+
+Run (from repo root):
+`dotnet test src/Concelier/__Tests/StellaOps.Concelier.Integration.Tests/StellaOps.Concelier.Integration.Tests.csproj`