message: network-grpc: #[must_use] on futures and streams
  The compiler will warn if a returned future or stream value is dropped
  without being used.
diff: @@ -33,6 +33,7 @@ impl<T: Node> NodeService<T> {
  }
  }
  +#[must_use = "futures do nothing unless polled"]
  pub enum ResponseFuture<T, F> {
  Pending(F),
  Failed(Status),
  @@ -59,6 +60,7 @@ impl<T, F> ResponseFuture<T, F> {
  }
  }
  +#[must_use = "futures do nothing unless polled"]
  pub enum SubscriptionFuture<T, Id, F> {
  Normal {
  inner: ResponseFuture<T, F>,
  @@ -176,6 +178,7 @@ where
  }
  }
  +#[must_use = "streams do nothing unless polled"]
  pub struct ResponseStream<T, S> {
  inner: S,
  _phantom: PhantomData<T>,
  @@ -218,6 +221,7 @@ where
  }
  }
  +#[must_use = "streams do nothing unless polled"]
  pub struct RequestStream<T, S> {
  inner: S,
  _phantom: PhantomData<T>,
  