Add Utils.retime to mimic karaoke templates (Kara-Templater reference)

Mimic Karaoke Templater `retime` Method Reference: [Kara-Templater retime implementation](https://github.com/slackingway/karaOK/blob/master/autoload/ln.kara-templater-mod.lua#L352) ## Proposal Implement a function `Utils.retime` in PyonFX to closely mimic the karaoke templating logic found in Kara-Templater. ### Usage Example ```python Utils.retime("start2syl", l, syl, start_offset=0, end_offset=0) ``` - `start2syl`: Mode to retime. - `l`: The line to apply the edits to. - `syl`: The syllable to use as data source. - `start_offset` and `end_offset`: Optional integer offsets for timing adjustment. ### Motivation This feature will allow users to more easily port karaoke templates from Kara-Templater to PyonFX, making script migration and compatibility smoother for advanced timing effects.