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

This will save us some copies, because a clone will simply create an
additional pointer to the same data.

Change-Id: I017a5d6b4c85a861b5541ebad2858ad4fbf8e8fa
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8978
Reviewed-by: raitobezarius <tvl@lahfa.xyz>
Autosubmit: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI

tvix/store/src/blobservice/sled.rs

@@ -136,8 +136,7 @@ impl BlobWriter for SledBlobWriter {
         } else {
             let (buf, hasher) = self.writers.take().unwrap();
 
-            // We know self.hasher is doing blake3 hashing, so this won't fail.
-            let digest = B3Digest::from_vec(hasher.finalize().as_bytes().to_vec()).unwrap();
+            let digest: B3Digest = hasher.finalize().as_bytes().into();
 
             // Only insert if the blob doesn't already exist.
             if !self.db.contains_key(digest.to_vec()).map_err(|e| {