test: verify Bazel cache reuse

[AlexanderLanin]

This intentionally no-op PR measures Bazel cache reuse in upstream CI. For the jobs that use eclipse-score/cicd-actions/setup-bazel-cache@cache, the unchanged source and build configuration should provide a clean cache-hit signal without introducing functional changes.

Changes:

• Adds one comment-only marker to .gitignore; no source, workflow, or build configuration is changed.
• Focuses analysis on the four build matrix executions and the coverage job that directly use setup-bazel-cache@cache.
• Leaves all other CI jobs outside the cache-focused result.