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

livekit-ffi/protocol/participant.proto

@@ -0,0 +1,22 @@
+syntax = "proto3";
+
+package livekit;
+option csharp_namespace = "LiveKit.Proto";
+
+//import "handle.proto";
+import "track.proto";
+
+message ParticipantInfo {
+  string sid = 1;
+  string name = 2;
+  string identity = 3;
+  string metadata = 4;
+  repeated TrackPublicationInfo publications = 5;
+}
+
+message ParticipantEvent {
+  string participant_sid = 1;
+  oneof message { IsSpeakingChanged speaking_changed = 2; }
+}
+
+message IsSpeakingChanged { bool speaking = 1; }