HLS: Tweak master segment storage and slave lookup

* HLS Segmenter: We no longer have a need to store the actual segment data in
  the finalizer.
* HLS Segmenter: Store `data_length`, `ts_actual` and `end_ts_actual` on the
  segment object so that they can be used on the slave side
* HLS Index: Look up segment audio using the more precise `ts_actual` instead
  of the `ts`. Should allow us to get exact index hits in the MemoryStore
  lookup instead of having to determine closest chunk.