Deferring side effecting code in `_Py_Dealloc()`

Currently _Py_Dealloc() can call arbitrary code, and since _Py_Dealloc() can be called by any Py_DECREF() is means that Py_DECREF() can call arbitrary code. Py_DECREF() is everywhere, so it impairs our ability to reason about about the behavior of code.
This problem is not as severe as https://github.com/python/cpython/issues/97922, but is still worth fixing, especially as it will impair our ability to optimize traces for 3.12.

We can either make a Py_SAFE_DECREF() to be used internally, or change Py_DECREF() to defer all potentially side-effecting deallocation functions.

It is not clear which is the best option. Changing Py_DECREF() is simple, and certainly easy to reason about, but might delay deallocation of extension module objects for too long.

Start by examining the _Py_Dealloc() and Py_DECREF() entry points referenced in the issue, then read issue 97922 for related context. Compare the proposed Py_SAFE_DECREF() approach with changing Py_DECREF() itself, including the effect on extension module object deallocation. Done means selecting and implementing a justified design with coverage for the resulting deallocation behavior.