fix(tvix/castore/import): symlink targets are Vec<u8>

These can be arbitrary bytes in theory. Some of our libraries might
be more strict, or inconsistent w.r.t. their representation of path
separators.

Change-Id: I7981b74fc7d3dd79f5589cf2ef52ced7b71dd003
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11551
Tested-by: BuildkiteCI
Reviewed-by: edef <edef@edef.eu>

tvix/castore/src/import/archive.rs

@@ -150,7 +150,9 @@ where
                 target: entry
                     .link_name()?
                     .ok_or_else(|| Error::MissingSymlinkTarget(path.clone()))?
-                    .into(),
+                    .into_owned()
+                    .into_os_string()
+                    .into_encoded_bytes(),
                 path,
             },
             // Push a bogus directory marker so we can make sure this directoy gets