feat(tvix/nix-compat): have StorePath accept bytes

The primary constructor for this is now from_bytes, from_string is
simply calling .as_bytes() on the string, passing it along.

The InvalidName error now contains a Vec<u8>, to encode the invalid name
(which might not be a string anymore).

from_absolute_path now accepts a &[u8] (even though we might want to
make this a OSString of some sort).

StorePath::validate_name has been degraded to a pub(crate) function.
It's still used in src/derivation, even though it probably shouldn't at
all - that cleanup is left for cl/8412 though.

Change-Id: I6b4e62a6fa5c4bec13b535279e73444f0b83ad35
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8973
Autosubmit: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI
Reviewed-by: raitobezarius <tvl@lahfa.xyz>

tvix/nix-compat/src/store_path/utils.rs

@@ -145,7 +145,7 @@ fn build_store_path_from_fingerprint_parts(
         hasher.finalize()
     };
     let compressed = compress_hash::<20>(&digest);
-    StorePath::validate_name(name)?;
+    super::validate_name(name.as_bytes())?;
     Ok(StorePath {
         digest: compressed,
         name: name.to_string(),