ruby : add Whisper::Token, fix model URI (#3575)

ruby : add Whisper::Token, fix model URI (#3575)

* Define and use macro to get context safely

* Add test to check SEGV

* Move installation guid after usage

* [skip ci]Change doc slightly

* [skip ci]Fix a typo in README

* [skip ci]Add carry_initial_prompt option in README

* Define GetVADSegments and use it

* Use GetContext

* Fix download URI of small.en-tdrz

* Fix URI of CoreML models corresponding to quantized models

* Cache computed string

* Remove unused argument

* Add Whisper::Token

* Add document comments

* Rename function: rb_whisper_token_s_new -> ruby_whisper_token_s_init

* Fix size of token

* Insert _get into function names

* Add Whisper::Token#text

* Add test for Whisper::Token#text

* Declare static if possible

* Change method names

* Add Whisper::Token#deconstruct_keys

* Add tests for Whisper::Token#deconstruct_keys

* Add signatures for Whisper::Token

* Complete signature

* [skip ci]Add n_tokens to document of Segment