`PackagePath` does not support Windows paths

[konstin]

Currently, importlib.metadata.files assumes that path are Unix-style with forward slashes, while the spec allows Windows-style backwards slashes too. This causes e.g. the .name on items to be inconsistent between platforms (astral-sh/uv#14446).

importlib_metadata/importlib_metadata/__init__.py

Line 371 in 95ecf2a

class PackagePath(pathlib.PurePosixPath):

From https://packaging.python.org/en/latest/specifications/recording-installed-packages/#the-record-file

The path may be either absolute, or relative to the directory containing the .dist-info directory (commonly, the site-packages directory). On Windows, directories may be separated either by forward- or backslashes (/ or ).

Ref #51