feat(tvix/castore/path): impl AsRef<Path> for Path

This allows using both Path and PathBuf in a function argument taking
`impl AsRef<Path>`.

Change-Id: Ibd3ba6fac538069d2fe729d1ef399fdef301668f
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11574
Tested-by: BuildkiteCI
Autosubmit: flokli <flokli@flokli.de>
Reviewed-by: Connor Brewster <cbrewster@hey.com>

tvix/castore/src/path.rs

@@ -117,6 +117,12 @@ impl Display for Path {
     }
 }
 
+impl AsRef<Path> for Path {
+    fn as_ref(&self) -> &Path {
+        self
+    }
+}
+
 /// Represents a owned PathBuf in the castore model.
 /// These are always relative, and platform-independent, which distinguishes
 /// them from the ones provided in the standard library.