partial __getstate__ wrong (?)

Bug report

Bug description:

The native _functools.partial type __getstate__ will return its __dict__. That will not include func, args or keywords.

This is different from the pure Python implementation of functools.partial (link), where it will return the slots, i.e. the state includes func, args or keywords.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

比較 _functools.partial getstate 的原生行為與 issue 中連結的純 Python functools.partial 實作，重點關注是否包含 func、args 和 keywords。追蹤現有的 partial 實作與測試，然後新增一個迴歸測試，定義預期的狀態並確認原生行為與純 Python 行為一致。