feat(mixer): enhance mixer functionality with interaction and tool legs

- Updated mixer to handle participant and isolated leg roles, allowing for IVR and consent interactions.
- Introduced commands for starting and canceling interactions, managing tool legs for recording and transcription.
- Implemented per-source audio handling for tool legs, enabling separate audio processing.
- Enhanced DTMF handling to forward events between participant legs only.
- Added support for PCM recording directly from tool legs, with WAV file generation.
- Updated TypeScript definitions and functions to support new interaction and tool leg features.

rust/crates/proxy-engine/src/webrtc_engine.rs

@@ -290,6 +290,8 @@ async fn browser_to_mixer_loop(
                         .send(RtpPacket {
                             payload: payload.to_vec(),
                             payload_type: PT_OPUS,
+                            marker: false,
+                            timestamp: 0,
                         })
                         .await;
                 }