fix(sglang): enable logprob parsing for SGLang client

[gowthamrao]

Fixes issue #128 by:

• Enabling return_logprob and top_logprobs_num=1 in SGLang request body.
• Robustly extracting logarithmic probabilities from input/output token logprobs in meta_info.
• Converting logarithmic values to linear probabilities via math.exp.
• Retaining hardcoded probabilities strictly as a fallback.
• Updating tests to inject logprob mock structures and assert correct propagation.

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PR created automatically by Jules for task 4781240915082436270 started by @gowthamrao

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