message: nydus-image: support copying v6 chunk from v5
  Now that the only difference is the wrapper, we can do the copying easily.
diff: @@ -1645,8 +1645,12 @@ impl ChunkWrapper {
  (ChunkWrapper::V6(s), ChunkWrapper::V6(o)) => {
  s.clone_from(o);
  }
  - (ChunkWrapper::V5(_s), ChunkWrapper::V6(_o)) => todo!(),
  - (ChunkWrapper::V6(_s), ChunkWrapper::V5(_o)) => todo!(),
  + (ChunkWrapper::V5(s), ChunkWrapper::V6(o)) => {
  + s.clone_from(o);
  + }
  + (ChunkWrapper::V6(s), ChunkWrapper::V5(o)) => {
  + s.clone_from(o);
  + }
  }
  }
  