gh-120754: _io Ensure stat cache is cleared on fd change (#125166)

gh-120754: _io Ensure stat cache is cleared on fd change (#125166)

Performed an audit of `fileio.c` and `_pyio` and made sure anytime the
fd changes the stat result, if set, is also cleared/changed.

There's one case where it's not cleared, if code would clear it in
__init__, keep the memory allocated and just do another fstat with the
existing memory.