Enhancement: audio speakers (#44)

* refactor: active speakers

1. Observe the loudest adjusted with active ratio instead of linear average of decibel values
2. Follow RFC6465 to convert audio level from decibel to linear value.
3. Quantize audio level for stable slice comparison
4. Switch moving average algorithm from MMA to EMA to have the same center of mass with SMA
5. Minor: remove seenSids map allocation
6. Minor: minimize division arithmetic

* Update pkg/rtc/audiolevel.go

Co-authored-by: David Zhao <david@davidzhao.com>

test/client/trackwriter.go

@@ -23,7 +23,6 @@ type TrackWriter struct {
 	track    *webrtc.TrackLocalStaticSample
 	filePath string
 	mime     string
-	done     chan bool
 
 	ogg       *oggreader.OggReader
 	ivfheader *ivfreader.IVFFileHeader
@@ -39,7 +38,6 @@ func NewTrackWriter(ctx context.Context, track *webrtc.TrackLocalStaticSample, f
 		track:    track,
 		filePath: filePath,
 		mime:     track.Codec().MimeType,
-		done:     make(chan bool),
 	}
 }