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

在 Python 3.12 和 3.13 上重現生成器表達式的行為，然後檢查 pathlib/_local.py 第 575 行附近的程式碼，以及 issue 74929 中討論的生成器表達式語意。確定變更後的求值順序是刻意如此還是回歸，並新增一個有針對性的回歸測試，展示 FileNotFoundError 預期發生的時機。