fix: return Ok(true) on ICE Disconnected to prevent resource leak

poll_rtc() always returned Ok(false), preventing WebRtcState from
clearing self.inner on disconnect. This leaked the UDP socket, Rtc
instance, and 65KB buffer permanently if the client never reconnected.

Closes #10

src/webrtc.rs

@@ -357,6 +357,7 @@ impl WebRtcInner {
                         Event::IceConnectionStateChange(IceConnectionState::Disconnected) => {
                             tracing::warn!("WebRTC disconnected");
                             self.connected = false;
+                            return Ok(true);
                         }
                         Event::MediaAdded(ma) => {
                             tracing::info!("Media added: mid={:?}", ma.mid);