GeezerVison

Use PyMem_* for allocating dict keys objects

Currently dict keys are allocated using PyObject_Malloc. This isn't right for free-threaded builds because we don't want non-object allocations to overlap with the object heap. Doing so breaks the guarantees that we can apply an incref to a value which may have been freed and back it out if we lost the reference to the logic. This just switches the allocations to use PyMem_* instead.

This also eliminates some duplication by moving the decref into dictkeys_decref when the ref count drops to zero. This is the only place we need to do this, but the logic to move to the free list or free is currently duplicated. This will become a little more complex with QSBR so we may as well isolate it all to one spot.

• Issue: Make dict objects thread-safe in --disable-gil builds #112075