Refactor Bazel CI job setup

[bolinfest]

Why

This stack adds a new Bazel CI lane that verifies Rust code behind cfg(not(debug_assertions)), but adding that job directly to .github/workflows/bazel.yml would duplicate the same setup in multiple places. Extracting the shared setup first keeps the follow-up change easier to review and reduces the chance that future Bazel workflow edits drift apart.

What Changed

• Added .github/actions/prepare-bazel-ci/action.yml as a composite action for the Bazel job bootstrap shared by multiple workflow jobs.
• Moved the existing Bazel setup, repository-cache restore, and execution-log setup behind that action.
• Updated the test and clippy jobs in .github/workflows/bazel.yml to call prepare-bazel-ci.
• Exposed repository-cache-hit and repository-cache-path outputs so callers can keep the existing cache-save behavior without duplicating the restore step.

Verification

• Parsed .github/workflows/bazel.yml as YAML locally after rebasing the stack.
• CI will exercise the refactored jobs end to end.

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Stack created with Sapling. Best reviewed with ReviewStack.

• Add Bazel verify-release-build job #17705
• -> Refactor Bazel CI job setup #17704