Close channel first before return undeliverable and remove log (#1879)

Summary:
Pull Request resolved: #1879

Two changes:

* Close NetTx's `mspc::Receiver` before returning the message. Otherwise, we might get stuck on this loop if there is another thread actively writing to this NetTx:

https://www.internalfb.com/code/fbsource/[5ee448cb323e2539ea2cf169644b7d829d715040]/fbcode/monarch/hyperactor/src/channel/net/client.rs?lines=586-590

New messages are still returned after `mspc::Receiver` is closed:

https://www.internalfb.com/code/fbsource/[5ee448cb323e2539ea2cf169644b7d829d715040]/fbcode/monarch/hyperactor/src/channel/net.rs?lines=156-161

* Remove the log when the return_channel is closed. This log does not seem to be helpful, and also we do not log it in other places for closed `return_channel`.

Reviewed By: mariusae

Differential Revision: D87002126

fbshipit-source-id: 69a7b57bc9addf1bdc62cfe324a45877421f6fb4

Author: pzhan9

hyperactor/src/channel/net/client.rs

@@ -576,6 +576,8 @@ async fn run<M: RemoteMessage>(
             // TODO(T233029051): Return reason through return_channel too.
             reason: _,
         } => {
+            // Close the channel to prevent any further messages from being sent.
+            receiver.close();
             // Return in order from oldest to newest, messages
             // either not acknowledged or not sent.
             unacked
@@ -584,9 +586,7 @@ async fn run<M: RemoteMessage>(
                 .chain(outbox.deque.drain(..))
                 .for_each(|queued| queued.try_return());
             while let Ok((msg, return_channel, _)) = receiver.try_recv() {
-                if let Err(m) = return_channel.send(SendError(ChannelError::Closed, msg)) {
-                    tracing::warn!("failed to deliver SendError: {}", m);
-                }
+                let _ = return_channel.send(SendError(ChannelError::Closed, msg));
             }
         }
         _ => (),