[Feature]: handle request parameter best_of=1

[tstescoTT]

🚀 The feature, motivation and pitch

Currently we do not support best_of parameter and setting it in the request will fail validation.

The sampling arg best_of appears to be handled as an int in client side code, e.g.:
https://github.com/tenstorrent/vllm/blob/dev/benchmarks/benchmark_serving.py#L784
so it gets set to 1 when turned off in some cases like this.

Ideally the default handling of best_of = 1 should be the same as best_of = None https://github.com/tenstorrent/vllm/blob/dev/vllm/sampling_params.py#L291.

Alternatives

No response

Additional context

Currently I need to patch the benchmarking script as a work around.

Before submitting a new issue...

• Make sure you already searched for relevant issues, and asked the chatbot living at the bottom right corner of the documentation page, which can answer lots of frequently asked questions.

[tstescoTT]

Also supporting default None or nop values for logprobs would similarly be useful and expected.