v0.25.2: DTS-HD codec ID + PGS BlockDuration

- MkvTrack::audio emits A_DTS/MA, A_DTS/HR, A_DTS per the DTS family
  instead of mislabelling everything as A_DTS. Plex transcoder and
  strict hardware decoders reject DTS-HD MA payload under a plain
  A_DTS track.
- PgsParser is now stateful: pairs display PCS with the following
  empty PCS to compute a duration. Frame::duration_ns + PesFrame::duration_ns
  carry it through; MkvMuxer::write_frame gains a final Option<u64>
  parameter that emits BlockGroup + BlockDuration when set. Fixes
  subtitle bitmaps lingering past their intended end-time.

src/mux/m2ts.rs

@@ -161,6 +161,7 @@ mod tests {
             pts: 0,
             keyframe: true,
             data: fake_idr_pes_data(),
+            duration_ns: None,
         };
         stream.write(&frame).unwrap();
         stream.finish().unwrap();