Import errors with loo long entry in sys.path or PYTHONPATH in Windows

Bug report

Bug description:

Having too long entries in sys.path or PYTHONPATH in Windows will cause different errors in imports. This was first reported on #122170, where there is some useful discussion.

> $Env:PYTHONPATH="a" * 33000
> py -3.13
Exception ignored in running getpath:
Traceback (most recent call last):
  File "<frozen getpath>", line 668, in <module>
OSError: failed to make path absolute
Fatal Python error: error evaluating path
Python runtime state: core initialized

Current thread 0x00005a8c (most recent call first):
  <no Python frame>

>>> import sys
>>> sys.path.insert(0, "a" * 33000)
>>> import email
Traceback (most recent call last):
  File "<frozen importlib._bootstrap_external>", line 1512, in _path_importer_cache
KeyError: 'aaaaaaaaaaaaaaaaaaaaaaaa[...]aaaaaaaaaa'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<python-input-6>", line 1, in <module>
    import email
  File "<frozen importlib._bootstrap>", line 1360, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1322, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 1262, in _find_spec
  File "<frozen importlib._bootstrap_external>", line 1555, in find_spec
  File "<frozen importlib._bootstrap_external>", line 1527, in _get_spec
  File "<frozen importlib._bootstrap_external>", line 1514, in _path_importer_cache
  File "<frozen importlib._bootstrap_external>", line 1490, in _path_hooks
  File "<frozen importlib._bootstrap_external>", line 1714, in path_hook_for_FileFinder
  File "<frozen importlib._bootstrap_external>", line 173, in _path_isdir
  File "<frozen importlib._bootstrap_external>", line 158, in _path_is_mode_type
  File "<frozen importlib._bootstrap_external>", line 152, in _path_stat
ValueError: stat: path too long for Windows

CPython versions tested on:

3.13, CPython main branch

Operating systems tested on:

Windows

Linked PRs

• gh-122389

从 issue 中的长路径复现开始，并检查 Windows 上 frozen getpath 和 importlib._bootstrap_external 的 traceback 位置。查看 issue #122170 和关联的 PR gh-122389，了解现有方向。当较长的 PYTHONPATH 和 sys.path 条目不再产生所报告的启动或导入错误时，即视为完成。