ruby : Add low-level methods to transcribe (#2585)

ruby : Add low-level methods to transcribe (#2585)

* Add tests for Whisper::Context#full

* Add Whisper::Context#full

* Add tests for Whisper::Error

* Add document of Whisper::Context#full [skip ci]

* Add additional signature for Whisper::Context#full

* Add description to Whisper::Context#full

* Add test for Whisper::Context#full_parallel

* Add Whisper::Context#full_parallel

* Hide Whisper's instance methods from Ruby code

* Add class to test MemoryView

* Build test class before running test

* Add test for MemoryView

* Make Whisper::Context#full and #full_parallel accept MemoryView

* Use Ruby 3.1 on CI

* Add comment on samples data type

* Update README

* Update README

* Remove unused code