* Refactor online recognizer.
Make it easier to support other streaming models.
Note that it is a breaking change for the Python API.
`sherpa_onnx.OnlineRecognizer()` used before should be
replaced by `sherpa_onnx.OnlineRecognizer.from_transducer()`.
* added csrc/stack.cc
* stack: added checks
* added copyright info
* passed cpp style checks
* formatted code
* added some support for streaming conformer model support (not verified)
* code lint
* made more progress with streaming conformer support (not working yet)
* passed style check
* changes as suggested by @csukuangfj
* added some debug info
* fixed style check
* Use Cat to replace Stack
* remove debug statements
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Co-authored-by: Jingzhao Ou (jou2019) <jou2019@cisco.com>
Co-authored-by: Fangjun Kuang <csukuangfj@gmail.com>
