ruby : bug fix on callbacks and no_speech_prob (#2656)

ruby : bug fix on callbacks and no_speech_prob (#2656)

* Don't generate documentation on test

* Move .startup to TestBase class

* Extract new_segment_callback as a function

* Extract progress_callback as a function

* Extract abort_callback as a function

* Extract register_callbacks as a function

* Call callbacks in Whiser::Context#full and #full_parallel

* Fix README

* Care about the cases content-size is nil and TTY is not available

* Add tests for no_speech_prob

* Add Whisper::Context#full_get_segment_no_speech_prob and Whisper::Segment#no_speech_prob