Expose rtc::Track with send(binary) for raw RTP — verified:
- SDP from addTrack(audio)+addTrack(video) has m=audio (opus 120)
and m=video (H264 101 + H265/VP8/VP9/AV1 + RTX)
- libdatachannel Track::send() sends RAW RTP/RTCP when no media
handler is set (verified in src/track.cpp impl::Track::outgoing) —
so RTP packetization can live in pure JS, keeping the binding minimal
Also fix: Track class was missing from InitAll exports (crash on
TrackWrap::NewInstance — null FunctionReference).
