Use a stack to implement os.walk iteratively instead of recursively to
avoid hitting recursion limits on deeply nested trees.

…2015)

Co-authored-by: Jelle Zijlstra <[email protected]>

Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>
Co-authored-by: Christian Heimes <[email protected]>
Co-authored-by: Hugo van Kemenade <[email protected]>
Fixes python#89051

…ions in imaplib docs (python#99625)

…with `_read_ready_cb` (python#100349)

…ythonGH-99926)

…ython#99246)

Make sure file descriptors get closed if an exception occurs right after the file descriptor was popped from the stack. Also catch exceptions thrown by calling os.close on an already-closed file-descriptor when doing file descriptor cleanup.

If an exception occurred between `close(fd_stack[-1])` and `fd_stack.pop()`, then we would close the fd a second time in the except clause. It would be better to risk leaving the fd open, as the previous implementation of fwalk could