private static MessageType marshallerType(Marshaller<?> marshaller) {
        return marshaller instanceof PrototypeMarshaller ? MessageType.PROTOBUF : MessageType.UNKNOWN;
    }
Marshaller for gRPC method request or response messages to and from {@link ByteBuf}. Will attempt to use
optimized code paths for known message types, and otherwise delegates to the gRPC stub.
grpc/src/main/java/com/linecorp/armeria/internal/common/grpc/GrpcMessageMarshaller.java