feat: add publishing & audio to ffi (#46)

- Divide FFI protocol into multiple files
- Audio support
- AV Streams/Sources
- Create tracks
- Use Dashmap to store handles
- Add a capture test
     - Ignored by GHA atm

webrtc-sys/src/video_frame.cpp

@@ -24,10 +24,10 @@ namespace livekit {
 VideoFrame::VideoFrame(const webrtc::VideoFrame& frame)
     : frame_(std::move(frame)) {}
 
-int VideoFrame::width() const {
+unsigned int VideoFrame::width() const {
   return frame_.width();
 }
-int VideoFrame::height() const {
+unsigned int VideoFrame::height() const {
   return frame_.height();
 }
 uint32_t VideoFrame::size() const {