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/proto/mod.rs

@@ -86,7 +86,7 @@ fn validate_node_name<E>(name: &[u8], err: fn(Vec<u8>) -> E) -> Result<(), E> {
 
 /// Checks a digest for validity.
 /// Digests are 32 bytes long, as we store blake3 digests.
-fn validate_digest<E>(digest: &Vec<u8>, err: fn(usize) -> E) -> Result<(), E> {
+fn validate_digest<E>(digest: &bytes::Bytes, err: fn(usize) -> E) -> Result<(), E> {
     if digest.len() != 32 {
         return Err(err(digest.len()));
     }