feat(tvix/eval): introduce ErrorKind::InvalidHash

The nixhash errors were wrapped in a generic TvixError. Now it has its
own TvixError with unique error code. The nixhash error is passed along
as a string.

The errors looked like:

error[E997]: invalid encoded digest length '51' for algo sha256

Now they look like:

error[E041]: Invalid hash: invalid encoded digest length '51' for algo
sha256

Change-Id: I5c420815538ba4c6567c95f5d44d60c4d48f43fd
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12718
Reviewed-by: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI

tvix/glue/src/builtins/fetchers.rs

@@ -73,8 +73,7 @@ async fn extract_fetch_args(
     let sha256 = match sha256_str {
         Some(sha256_str) => {
             let nixhash = nixhash::from_str(&sha256_str, Some("sha256"))
-                // TODO: DerivationError::InvalidOutputHash should be moved to ErrorKind::InvalidHash and used here instead
-                .map_err(|e| ErrorKind::TvixError(Rc::new(e)))?;
+                .map_err(|e| ErrorKind::InvalidHash(e.to_string()))?;
 
             Some(nixhash.digest_as_bytes().try_into().expect("is sha256"))
         }