feat(asr): improve subtitle cue formatting

[hyperpuncher]

summary

Make SRT and WebVTT subtitles easier to read by using one formatter for both the command line and HTTP API.

Previously, command-line subtitles could produce long single-line cues, reaching 83 characters in the one-minute test. HTTP responses could also place a whole recording in one subtitle.

The formatter:

• splits subtitles at sentences, clauses, and pauses
• uses up to two lines, targeting 37 characters and generally staying within 42 without breaking words
• sets display time based on a reading speed of about 180 words per minute
• displays each subtitle for 5/6 of a second to 7 seconds where timing permits
• keeps the recognized text unchanged

These readability targets are informed by the
BBC subtitle guidelines
and Netflix's
general timed-text requirements
and
timing guidelines.
They are not a claim of full BBC or Netflix compliance.

provenance

The subtitle splitting and line wrapping were adapted from my MIT-licensed
chough formatter.

I own the copyright to that implementation and submit this C++ adaptation under this repository's Apache 2.0 license.