[Feature] Add a function to convert sampling_params to kwargs

[gryffindor-rr]

Motivation

Modifications

add a function to convert params to a dict to adapt different arg names.

Checklist

• Format your code according to the Contributor Guide.
• Add unit tests as outlined in the Contributor Guide.
• Update documentation as needed, including docstrings or example tutorials.

[JianyuZhan]

I also mentioned this circuitous transfrom from SamplingParams class to SamplingParams dict and then to SamplingParams class in my pending PR. I also added a to_dict transform method. I think the better way is when SamplingParams is promoted as a publically accessible API, then do away this cubesome transform.

[zhyncs]

Does stop_strs need to be processed as a list, in the case of multiple stop str scenarios?

[gryffindor-rr]

stop is either str or list of str, both type can be handled by json.dumps. the token_ids is a set which need to be converted to list.