Ability to weakly reference an instance of a class lost due to mutliple inheritance

This is related to https://github.com/python/cpython/issues/95589 due to underlying mechanism, but the behavior is distinct.

class C: 
    pass

class D(int, C):
    pass
>>> c = C()
>>> weakref.ref(c)
<weakref at 0x7fa5b2af9c60; to 'C' at 0x7fa5b2e501c0>
>>> d = D()
>>> weakref.ref(d)
TypeError: cannot create weak reference to 'D' object
>>> isinstance(d, C)
True

If I can weakly reference an instance of C, then I should be able to weakly reference an instance of D. Instances of D are instances of C

先使用類別 C 和 D 執行 issue 的 Python 重現程式，檢查每個執行個體的 weakref.ref 行為。追蹤 CPython 對涉及多重繼承的執行個體進行弱參照處理的過程；當 D 執行個體能以與其 C 基底類別一致的方式進行弱參照時，即視為完成。