chore: add scripts for reporting new contributors and code review statistics

[westonpace]

These are just some handy scripts for looking at community health.

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I used Claude Opus 4.5 (claude-opus-4-5-20251101) in the creation of these scripts. I have reviewed the contents and take full responsibility for them.

[github-actions]

Code Review

Overall: These are straightforward utility scripts for community health tracking. The code is clean and well-structured. A few observations:

P1 Issues

1. review_stats.py - Cache invalidation missing: The PR review cache (pr_reviews) grows unbounded and stores stale data forever. Old PRs remain cached even after the 30-day window passes. Consider:

   • Adding a timestamp to cached entries and purging entries older than 30 days
   • Or simply not caching PR reviews since the data changes over time (reviews can be added after merge)

2. new_contributors.py - Potential false positives: Contributors whose email cannot be resolved to a GitHub username are included in the output with "(unknown)" username. These could be collaborators with write access who simply used a different email. The script's current logic includes them as "non-write contributors" which may overcount community contributions. Consider adding a note in the output or filtering these separately.

Minor Observations (not blocking)

• Both scripts duplicate get_collaborators_with_write() - could be extracted to a shared module if more scripts are added later
• No --help or argument parsing, but acceptable for internal utility scripts

No security concerns. No test coverage, but these are developer tools not part of the main codebase.