Cache the match object in the compiled re pattern

Feature or enhancement

Proposal:

re allocates a new match object for every successful match. Matches of one pattern all have the same size, and in a typical loop the previous match dies just before the next one is created.

Keep one dead match object in the compiled pattern and reuse it for the next match instead of allocating. This saves 15-18 ns per successful match (e.g. p.match('42') goes 89 ns → 71 ns, and the string-to-Fraction constructor gains ~6%), with no behavior change. The cache slot is accessed with atomic operations; validated with the test suite, refleak runs, and a concurrent stress test on the free-threaded build.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Linked PRs

• gh-153162

從已編譯的 re 模式實作開始，檢查成功比對是如何配置的。使用現有測試套件確認行為維持不變，然後在 free-threaded 建置上執行 refleak 檢查和並行壓力測試。當已失效的比對物件能安全地重複使用，且所報告的效能提升得以維持時，即視為完成。