poor scaling of `functools.lru_cache`

functools.lru_cache currently scales poorly in free-threading because of reference counting contention on the object. The underlying function has deferred reference counting enabled but the cache object itself needs deferred reference counting as well to perform well in free-threading.

Linked PRs

• gh-142632

先檢視 functools.lru_cache 的實作與相關的 PR gh-142632，接著研究 free-threading 如何影響 cache 物件的參照計數。當 cache 在 free-threading 下能更好地擴充，同時保留 lru_cache 既有的行為與測試時，即表示完成。