fix(tvix/nar-bridge): Remove name check for root node in nar generation

Nar-bridge tried to parse the name of the protobuf node encoded in the
URL into a PathComponent but this name was empty, leading to an error
when the user tried to retrieve the nar file.

This was an oversight from the conversion to stricter types (some of the
CLs in the serious containing cl/12217).

We need a version converting a protobuf without a name to our stricter
types, but an empty PathComponent cannot be constructed.

So we need a into_name_and_node() version that returns the name as
Bytes, not PathComponent.

Change-Id: I2996cdd2e0107133e502748947298f512f1cc521
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12504
Reviewed-by: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI

tvix/castore/src/errors.rs

@@ -45,8 +45,8 @@ pub enum DirectoryError {
     #[error("{:?} is a duplicate name", .0)]
     DuplicateName(PathComponent),
     /// Node failed validation
-    #[error("invalid node with name {}: {:?}", .0, .1.to_string())]
-    InvalidNode(PathComponent, ValidateNodeError),
+    #[error("invalid node with name {}: {:?}", .0.as_bstr(), .1.to_string())]
+    InvalidNode(bytes::Bytes, ValidateNodeError),
     #[error("Total size exceeds u64::MAX")]
     SizeOverflow,
     /// Invalid name encountered