gh-149474: use `Py_fopen` in `Binary{Reader,Writer}` for audit hook and path-like support (GH-149524)
(cherry picked from commit 354ef336e4)
Co-authored-by: Maurycy Pawłowski-Wieroński <maurycy@maurycy.com>
Compute ``final_depth`` in ``decode_stack_pop_push()`` and
``decode_stack_suffix()`` using ``uint64_t`` before validating it.
On 32-bit builds, using ``size_t`` arithmetic for ``keep + push`` can wrap
for large input values, causing the later bounds check to validate the wrong
final depth. Using a widened type keeps the validation aligned with the
actual result.
