[3.12] GH-89727: Fix `os.fwalk()` recursion error on deep trees (GH-119638) (#119765)

GH-89727: Fix `os.fwalk()` recursion error on deep trees (GH-119638)

Implement `os.fwalk()` using a list as a stack to avoid emitting recursion
errors on deeply nested trees.
(cherry picked from commit 3c890b503c740767d0eb9a0e74b47f17a1e69452)

Co-authored-by: Barney Gale <barney.gale@gmail.com>