Pathlib.iterdir semantics change dramatically under Python 3.13

Bug report

Bug description:

This code behaves very differently on Python 3.13 than 3.12:

(p for p in pathlib.Path('does-not-exist').iterdir())

 🐚 py -3.12 -c "import pathlib; (p for p in pathlib.Path('does-not-exist').iterdir())"
 🐚 py -3.13 -c "import pathlib; (p for p in pathlib.Path('does-not-exist').iterdir())"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
    import pathlib; (p for p in pathlib.Path('does-not-exist').iterdir())
                                ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^
  File "/opt/homebrew/Cellar/python@3.13/3.13.1/Frameworks/Python.framework/Versions/3.13/lib/python3.13/pathlib/_local.py", line 575, in iterdir
    with os.scandir(root_dir) as scandir_it:
         ~~~~~~~~~~^^^^^^^^^^
FileNotFoundError: [Errno 2] No such file or directory: 'does-not-exist'

In Python 3.12, the generator expression was evaluated lazily, not invoking path.iterdir() until the generator was consumed. On 3.13, at least a portion of the generator is evaluated, triggering the exception when the dir does not exist.

I discovered this issue in https://github.com/jaraco/jaraco.develop/issues/26.

I looked at What's New for Python 3.13, and there's only one mention of generator expressions regarding mutation of locals in generator expressions, which doesn't seem to be relevant here.

That change mentions https://github.com/python/cpython/issues/74929, so maybe that change is also implicated in the change in execution order.

CPython versions tested on:

3.13

Operating systems tested on:

macOS

Reproduisez le comportement des expressions génératrices avec Python 3.12 et 3.13, puis inspectez pathlib/_local.py autour de la ligne 575 ainsi que la sémantique des expressions génératrices abordée dans issue 74929. Déterminez si l’ordre d’évaluation modifié est intentionnel ou s’il s’agit d’une régression, et ajoutez un test de régression ciblé montrant le moment attendu du FileNotFoundError.