Make `os.scandir` retry on system calls failing with EINTR

Bug report

Bug description:

In a long-running script, I hit:

[…]
  File "/Users/gsnedders/ct.py", line 104, in worker
    with os.scandir(path) as it:
         ~~~~~~~~~~^^^^^^
InterruptedError: [Errno 4] Interrupted system call: '/Users/gsnedders/Library/Containers/com.apple.ScreenTimeWidgetApplication.ScreenTimeWidgetExtension/Data/Library/Application Scripts'

No repro case is provided, because that would require making syscalls fail with EINTR reliably somehow.

PEP 475 (Retry system calls failing with EINTR) implies to me that os.scandir should be retrying, rather than just failing here.

It does appear that os.scandir doesn't always retry, looking at the source:

https://github.com/python/cpython/blob/ae3064608935367c860182dc1b364631082ecdff/Modules/posixmodule.c#L16489

The iterator itself also seems to not retry:

https://github.com/python/cpython/blob/ae3064608935367c860182dc1b364631082ecdff/Modules/posixmodule.c#L16290

CPython versions tested on:

3.13

Operating systems tested on:

macOS

阅读 PEP 475 以及 Modules/posixmodule.c 中链接的 os.scandir 实现，包括所引用行中的迭代器代码。检查返回 EINTR 的系统调用是如何处理的，并验证 os.scandir 会重试，而不是引发 InterruptedError。只有初始调用和迭代器行为都符合预期的重试策略，才算完成。