Clone uses proto.Clone to return a deep copy of pb.

Marshal uses proto.Marshal to encode pb into the wire format.

Interceptor will be called with every proto before it is marshalled.

ProtoPb is a gwruntime.Marshaler that uses github.com/gogo/protobuf/proto.

JSONPb is a gwruntime.Marshaler that uses github.com/gogo/protobuf/jsonpb.