Improve progress bar progression for smaller voice messages

Instead of chunking the thing, we'll improve our precision and clock accuracy. Clock accuracy is improved by flagging the "load time" of the clip in the context, which can be about 500ms (or more) off the context's start line. The precision is just a number in the PlaybackWaveform component.

src/voice/Playback.ts

@@ -126,6 +126,7 @@ export class Playback extends EventEmitter implements IDestroyable {
         this.waveformObservable.update(this.resampledWaveform);
 
         this.emit(PlaybackState.Stopped); // signal that we're not decoding anymore
+        this.clock.flagLoadTime(); // must happen first because setting the duration fires a clock update
         this.clock.durationSeconds = this.audioBuf.duration;
     }