
This fixes two things in one go: 1. In order to indicate 'end of a cue' **without** relying on `CuesWithTiming.durationUs`, `SubripParser` should have been emitting an empty `List<Cue>` instead of the current behaviour of a single-item list with `cue.text=""`. 2. There's no need for the empty cue (or cue list), we can use `durationUs` to indicate the end of each list of cues. There's no real need to ever have a `Cue` with `text=""`, so also deprecate `Cue.EMPTY`. PiperOrigin-RevId: 548938874