gh-142731: Prevent use-after-free in _PyObject_StoreInstanceAttribute with re-entrant __hash__

[VanshAgarwal24036]

Fix a potential use-after-free when storing or deleting instance attributes if a re-entrant __hash__ mutates the instance __dict__ during attribute handling.

Temporarily INCREF the managed dict in the Py_GIL_DISABLED path to ensure it remains alive across the call to store_instance_attr_dict().

• Issue: Use-after-free in builtin_delattr_impl and builtin_setattr_impl via re-entrant __hash__ #142731

[picnixz]

What is the performance impact on this change? @kumaraditya303 hinted that this could add overhead (probably in free-threaded build) so I wpuld like that you first read the concerns on the issue before jumping on the PR. Serhiy also suggested an alternative.

[picnixz]

FTR this could impact dataclass creations, namedtuple creations and other types that are dynamically created or that heavily use setattr/delattr explicitly.