[3.14] GH-133789: Fix unpickling of pathlib objects pickled in Python 3.13 (GH-133831)

[miss-islington]

In Python 3.13 (but not 3.12 or 3.14), pathlib classes are defined in
pathlib._local rather than pathlib. In hindsight this was a mistake,
but it was difficult to predict how the abstract/local split would pan out.

In this patch we re-introduce pathlib._local as a stub module that
re-exports the classes from pathlib. This allows path objects pickled in
3.13 to be unpicked in 3.14+
(cherry picked from commit f4e51f2)

Co-authored-by: Barney Gale [email protected]

• Issue: Pickled files with pathlib.Path cannot be loaded in py >= 3.13 #133789