docs: public static <ReqT, RespT> ListenableFuture<RespT> futureUnaryCall(
        ClientCall<ReqT, RespT> call, ReqT req) {
      GrpcFuture<RespT> responseFuture = new GrpcFuture<>(call);
      asyncUnaryRequestCall(call, req, new UnaryStreamToFuture<>(responseFuture), false);
      return responseFuture;
    }