fix(swarm): implement ConnectionHandler::poll_close for combinators

Follow-up to libp2p#4076.

This is especially relevant since `libp2p-swarm-derive` uses `SelectConnectionHandler`.

swarm/src/behaviour/toggle.rs

@@ -369,4 +369,12 @@ where
             }
         }
     }
+
+    fn poll_close(&mut self, cx: &mut Context<'_>) -> Poll<Option<Self::ToBehaviour>> {
+        if let Some(inner) = self.inner.as_mut() {
+            inner.poll_close(cx)
+        } else {
+            Poll::Ready(None)
+        }
+    }
 }

swarm/src/handler/either.rs

@@ -142,6 +142,20 @@ where
         Poll::Ready(event)
     }
 
+    fn poll_close(
+        &mut self,
+        cx: &mut Context<'_>,
+    ) -> Poll<Option<Self::ToBehaviour>> {
+        let event = match self {
+            Either::Left(handler) => futures::ready!(handler.poll_close(cx))
+                .map(Either::Left),
+            Either::Right(handler) => futures::ready!(handler.poll_close(cx))
+                .map(Either::Right),
+        };
+
+        Poll::Ready(event)
+    }
+
     fn on_connection_event(
         &mut self,
         event: ConnectionEvent<

swarm/src/handler/map_in.rs

@@ -86,6 +86,13 @@ where
         self.inner.poll(cx)
     }
 
+    fn poll_close(
+        &mut self,
+        cx: &mut Context<'_>,
+    ) -> Poll<Option<Self::ToBehaviour>> {
+        self.inner.poll_close(cx)
+    }
+
     fn on_connection_event(
         &mut self,
         event: ConnectionEvent<

swarm/src/handler/map_out.rs

@@ -90,6 +90,12 @@ where
         })
     }
 
+    fn poll_close(&mut self, cx: &mut Context<'_>) -> Poll<Option<Self::ToBehaviour>> {
+        self.inner
+            .poll_close(cx)
+            .map(|ev| ev.map(|ev| (self.map)(ev)))
+    }
+
     fn on_connection_event(
         &mut self,
         event: ConnectionEvent<