fix(stats-fetcher): use GraphQL for accurate commit counts

[AdiGaikwad]

📌 Summary

Previously, total commits were fetched using the GitHub REST Search API.
This approach had two major issues:

• Capped at 1000 results - incomplete data for active contributors
• Inaccurate Commit Totals - inaccurate commit totals were given

✅ Changes

• Replaced REST commit fetching with a GraphQL query for accurate commit counts
• Updated unit tests & mocks to reflect GraphQL responses

🧪 Testing

• Verified commit counts for accounts with >10k commits
• All unit tests pass locally (npm test)
• Confirmed caching and error message behavior in /api endpoints

📂 Files Changed

1. src/fetchers/stats-fetcher.js → Implemented GraphQL commit fetching logic
2. tests/fetchStats.test.js → Updated commit mocks & assertions

🔗 Related Issues

Fixes #3850

[vercel]

@AdiGaikwad is attempting to deploy a commit to the github readme stats Team on Vercel.

A member of the Team first needs to authorize it.