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

将 _functools.partial getstate 的原生行为与 issue 中链接的纯 Python functools.partial 实现进行比较，重点关注是否包含 func、args 和 keywords。跟踪现有的 partial 实现和测试，然后添加一个回归测试，定义预期的状态并确认原生行为与纯 Python 行为一致。