Avoid canonicalizing executables on Windows (#5446)

## Summary

If you have an executable path on a network share path (like
`\\some-host\some-share\...\python.exe`), canonicalizing it adds the
`\\?` prefix, but dunce cannot safely strip it.

This PR changes the Windows logic to avoid canonicalizing altogether. We
don't really expect symlinks on Windows, so it seems unimportant to
resolve them.

Closes: https://github.com/astral-sh/uv/issues/5440.

crates/uv-cache/src/timestamp.rs

@@ -15,7 +15,7 @@ pub struct Timestamp(std::time::SystemTime);
 impl Timestamp {
     /// Return the [`Timestamp`] for the given path.
     pub fn from_path(path: impl AsRef<Path>) -> std::io::Result<Self> {
-        let metadata = path.as_ref().metadata()?;
+        let metadata = fs_err::metadata(path.as_ref())?;
         Ok(Self::from_metadata(&metadata))
     }