Optimize benchmarks pipeline, fix quota leaks and handle manual builds

[Mahalaxmibejugam]

This PR improves the robustness and maintainability of the benchmarks Cloud Build pipeline in benchmarks-cloudbuild.yaml

• Optimized Empty File Handling: Updated logic to use pipe() instead of open() + info() for empty files, reducing overhead and improving performance of read benchmarks.
• Fixed Quota Issues: Added a cleanup-leaked-resources step at the beginning of the build to find and delete leaked VMs (older than 5 hours) with the prefix ${_INFRA_PREFIX}-vm-. This prevents failed or cancelled builds from exhausting project quotas.
• Reduced Code Duplication: Combined the create-io-vm and create-metadata-vm steps into a single reusable create-vm step. It uses bash conditions to apply high-performance flags (like hyperdisk and GVNIC) only when _BENCHMARK_TYPE is IO.
• Fixed Manual Build Failures: Added a conditional check during the installation of gcsfs on the VM. If the .git directory is missing (which happens during manual gcloud builds submit runs), it sets a dummy version 0.0.0 to prevent hatch-vcs from failing.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.13%. Comparing base (94efa8c) to head (48e30de).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #851   +/-   ##
=======================================
  Coverage   89.13%   89.13%           
=======================================
  Files          15       15           
  Lines        3130     3130           
=======================================
  Hits         2790     2790           
  Misses        340      340           

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