Allow `--with-requirements` to load extensionless inline-metadata scripts (#16744)
Resolves https://github.com/astral-sh/uv/issues/16732
This diff treats extensionless files that contain
[PEP 723](https://peps.python.org/pep-0723/) metadata as scripts when
resolving `--with-requirements`, so inline metadata works even when the
script doesn’t end in `.py`.
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Co-authored-by: Charlie Marsh <charlie.r.marsh@gmail.com>