[Whisper Tokenizer] Encode timestamps (#26054)
* [Whisper Tokenizer] Fix tests after adding timestamps
* fix s2t tokenizer tests
* fix vocab test
* backwards comp
* fix tests
* comment
* style
* fix last test
* fix fast
* make faster
* move logic to decode
* remove skip test
* fix decode with offsets
* fix special tokens
* empty commit to re-trigger ci
* use lru cache
