feat(swarm): expose ConnectionId and add conn duration metric

- Exposes the `ConnectionId` in the various `SwarmEvent` variants.
- Tracks connection duration in `libp2p-metrics::swarm`.

Pull-Request: #3927.

examples/file-sharing/src/network.rs

@@ -329,7 +329,10 @@ impl EventLoop {
                 }
             }
             SwarmEvent::IncomingConnectionError { .. } => {}
-            SwarmEvent::Dialing(peer_id) => eprintln!("Dialing {peer_id}"),
+            SwarmEvent::Dialing {
+                peer_id: Some(peer_id),
+                ..
+            } => eprintln!("Dialing {peer_id}"),
             e => panic!("{e:?}"),
         }
     }