feat(tvix/store/proto): use Bytes instead of Vec<u8>

Makes use of https://github.com/tokio-rs/prost/pull/341, which makes our
bytes field cheaper to clone.

It's a bit annoying to configure due to
https://github.com/hyperium/tonic/issues/908, but the workaround does
get the job done.

Change-Id: I25714600b041bb5432d3adf5859b151e72b12778
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8975
Reviewed-by: raitobezarius <tvl@lahfa.xyz>
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>
Autosubmit: flokli <flokli@flokli.de>

tvix/store/src/directoryservice/traverse.rs

@@ -108,7 +108,7 @@ mod tests {
         let node_directory_complicated =
             crate::proto::node::Node::Directory(crate::proto::DirectoryNode {
                 name: "doesntmatter".into(),
-                digest: DIRECTORY_COMPLICATED.digest().to_vec(),
+                digest: DIRECTORY_COMPLICATED.digest().into(),
                 size: DIRECTORY_COMPLICATED.size(),
             });