ci: dump sccache logs on integration failures

[JalenBuildsHub]

The integration matrix currently loses the sccache server diagnostics when a test container fails. This enables a debug log for every integration test container, persists it through the existing coverage bind mount, clears the append-only log before each subtest, and prints the failing subtest's log from the job on failure.

Fixes #1685

Validated with Compose expansion across all 18 test services, Actionlint, both branches of the failure-log shell block, and cargo fmt -- --check. Native Clippy/tests were not completed locally because this Windows machine does not have the MSVC link.exe; the PR's Linux CI will run them.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.35%. Comparing base (6089d04) to head (db13a7a).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2851      +/-   ##
==========================================
- Coverage   76.22%   75.35%   -0.87%     
==========================================
  Files          72       72              
  Lines       39890    39890              
==========================================
- Hits        30406    30059     -347     
- Misses       9484     9831     +347     

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