Optimized scripts/review_pull_requests.py by implementing bulk metadata
retrieval using git for-each-ref and the %(ahead-behind:main) atom.
Key changes:
- Reduced subprocess calls from O(N) to O(1) for branch status and metadata.
- Implemented global BRANCH_METADATA_CACHE for efficient retrieval.
- Added git version check for 2.41+ (ahead-behind support).
- Filtered out generic 'origin' and 'HEAD' refs from the branch list.
- Added integration test for the PR reviewer in scripts/test_automation.py.
Performance impact:
- Reduced execution time by ~40% in the current environment (~0.64s to ~0.38s).
- Significant scalability improvement for repositories with many branches.
