`renderVTTTokensString` does not pass currentTime to recursive call

[jaco-terbraak]

VTT files can have cue payloads with nested timestamps. However renderVTTTokensString only processes the top-level timestamp according to the passed currentTime. It does not pass the currentTime to the recursive calls, so the nested timestamps don't get the appropriate date-future and date-past attributes.

See: https://github.com/vidstack/captions/blob/main/src/vtt/render-cue.ts#L60