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

コンパイル済み re パターンの実装から始め、成功したマッチがどのように割り当てられるかを調べます。既存のテストスイートを使って動作が変わらないことを確認し、その後、free-threaded ビルドで refleak チェックと並行ストレステストを実行します。デッドマッチオブジェクトが安全に再利用され、報告されたパフォーマンス向上が維持されれば完了です。