Specialized `match_keys` for exact dictionary type

Feature or enhancement

I think it's probably worthwhile to write a specialized version of match_keys (for structural pattern matching of mappings) for exact dictionary types

Pitch

The most common mapping type is almost certainly the built-in dict. The match_keys function in ceval.c could be specialized to handle this type. Doing so would allow you to skip the dummy object, and replace the get call with PyDict_GetItemWithError. I don't think this should change the observable behaviour at all for exact dict

I'm in the process of reimplementing structural pattern matching on Cython, and this change gives ~2x optimization of some microbenchmarks.

If this change is deemed desirable I'm happy to implement it myself.

Previous discussion

Not aware of any

從 ceval.c 中的 match_keys 開始，檢查 structural pattern matching 目前如何處理 mapping 鍵和精確的 dict 型別。當精確的 dict 使用專用路徑，同時不改變可觀察行為（包括現有的查找語義）時，修改就完成了；如果有可用的相關微基準，請進行比較。