refactor(tvix/castore): add try_into_anonymous_node, rename to try_*

We have two places where we parse protos and want their names to be
empty:

 - Receiving a root node in a nar-bridge NAR request
 - Processing the CalculateNAR gRPC call

We don't have any place where we want to keep a name as bytes::Bytes
around, yet we used the `into_name_bytes_and_node` method.

It was also a bit wrongly named - it wasn't very clear the name was
not validated, and that the function may fail.

This moves the "splitting off the name as bytes::Bytes" part into a
private helper, only leaving the `try_into_name_and_node` and
`try_into_anonymous_node` methods around.

Change-Id: I2c7fd9871d49ec67450d7efa6a30d96197fb319c
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12664
Autosubmit: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI
Reviewed-by: Marijan Petričević <marijan.petricevic94@gmail.com>
Reviewed-by: raitobezarius <tvl@lahfa.xyz>

tvix/store/src/proto/grpc_pathinfoservice_wrapper.rs

@@ -77,9 +77,9 @@ where
         &self,
         request: Request<castorepb::Node>,
     ) -> Result<Response<proto::CalculateNarResponse>> {
-        let (_, root_node) = request
+        let root_node = request
             .into_inner()
-            .into_name_bytes_and_node()
+            .try_into_anonymous_node()
             .map_err(|e| {
                 warn!(err = %e, "invalid root node");
                 Status::invalid_argument("invalid root node")

tvix/store/src/proto/mod.rs

@@ -274,7 +274,7 @@ impl TryFrom<PathInfo> for crate::pathinfoservice::PathInfo {
         let (name, node) = value
             .node
             .ok_or_else(|| ValidatePathInfoError::NoNodePresent)?
-            .into_name_and_node()
+            .try_into_name_and_node()
             .map_err(ValidatePathInfoError::InvalidRootNode)?;
 
         Ok(Self {