…FW3ZD.rst

Co-authored-by: Sergey Miryanov <sergey.miryanov@gmail.com>

…ternal helper and add unit tests

Extract the duplicated static `ptr_wise_atomic_memmove` from
`Modules/_elementtree.c` and `Objects/listobject.c` into a shared
`static inline _Py_ptr_wise_atomic_memmove(PyObject *a, ...)` in
`Include/internal/pycore_object.h`.  The first parameter is generalised
from a type-specific pointer to `PyObject *` since only `PyObject *`-
level operations (`_Py_IsOwnedByCurrentThread`, `_PyObject_GC_IS_SHARED`)
were ever performed on it.

`listobject.c` previously embedded `_Py_CRITICAL_SECTION_ASSERT_OBJECT_LOCKED`
inside the local helper.  That assertion is preserved by moving it
explicitly to each of the four call sites in `listobject.c` (which are
all called under a critical section).  `_elementtree.c`'s open question
about whether a critical section is needed remains unanswered, so no
assertion is added there.

Unit tests are added in `Modules/_testinternalcapi/test_ptr_wise_memmove.c`
covering: dest < src (forward copy), dest > src (backward copy),
dest == src (no-op), overlapping ranges, and the single-owner fast path.
The single-owner test explicitly clears the GC SHARED bit to guard against
freelist reuse leaving the bit set from a sibling test.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Commented out critical section assertion for ElementObject.

…e-149965.edk2ut.rst

This reverts commit a3a7eee.