[build] Surface Bazel cache failures with diagnostics and graceful fallback - #17541

Summary

• Add continue-on-error: true and id: setup-bazel-cached to the "Setup Bazel with caching" step so a cache failure no longer silently kills the job
• Add a "Report Bazel cache setup failure" step that fires on failure and emits a ::warning:: annotation with a disk space snapshot (both workspace and C: on Windows) so the cause is visible in the job summary
• Expand the "Setup Bazel without caching" condition to also run as a fallback when the cached setup fails, so the build continues and the actual test/build result is still visible

Motivation

setup-bazel@0.19.0 has been failing silently on Windows with no output — the step just shows as failed with no error message or context. This makes it impossible to diagnose whether the cause is disk pressure, a GitHub Actions cache service blip, or something else. With this change, cache failures surface a warning with disk space info and the job continues rather than dying before Bazel even runs.