fix: do a best-effort transmit on connection close

If we're shutting down ungracefully, we can make a best-effort attempt
to write the CONNECTION_CLOSE to the socket and notify the peer. If
we're in the middle of graceful shutdown, it doesn't hurt, either.

Author: colinmarc

noq/src/connection.rs

@@ -1233,6 +1233,14 @@ impl Drop for ConnectionRef {
             // be constructed for the newly opened stream.
             conn.implicit_close(&self.shared);
         }
+
+        // We also flush any pending packets, e.g. the CONNECTION_CLOSE, if we're able to do so
+        // synchronously. This is best-effort; we won't wait for them to be acked, but we have a
+        // decent chance of notifying the peer in the case that we're currently shutting down
+        // ungracefully.
+        let waker = std::task::Waker::noop();
+        let mut cx = std::task::Context::from_waker(waker);
+        let _ = conn.drive_transmit(&mut cx);
     }
 }
 
@@ -1709,6 +1717,7 @@ impl State {
     fn close(&mut self, error_code: VarInt, reason: Bytes, shared: &Shared) {
         self.inner.close(self.runtime.now(), error_code, reason);
         self.terminate(ConnectionError::LocallyClosed, shared);
+
         self.wake();
     }