Add configurable max pause to subtitles

[Cynary]

Proposed changes

It would be good to have the ability to split subtitles based on the amount of time between words.

Context

Today, if there's a big gap in time between two words, the subtitle just lingers in the screen, which can be distracting. Instead, it would be better for the subtitle to finish where the gap starts.

Possible Implementation

Should be similar to how you implement the line_length-based splitting, just look at the most recent word end time and compare it to the current start time.