Update logprobs handling

[oesni]

Fix issues on logprobs request.

stream response is like

{
    "id": "f9873c36-67c2-445e-92a6-6646a0b31304",
    "object": "chat.completion.chunk",
    "created": 1723180270,
    "model": "model-name",
    "choices": [
        {
            "index": 0,
            "delta": {
                "content": "Hello!"
            },
            "finish_reason": null,
            "logprobs": {
                "content": [
                    {
                        "token": "Hello",
                        "logprob": -0.10208277,
                        "bytes": [
                            72,
                            101,
                            108,
                            108,
                            111
                        ],
                        "top_logprobs": [],
                        "token_id": 16230,
                        "text_offset": 0
                    },
                    {
                        "token": "!",
                        "logprob": -0.02145231,
                        "bytes": [
                            33
                        ],
                        "top_logprobs": [],
                        "token_id": 28808,
                        "text_offset": 5
                    }
                ]
            }
        }
    ],
    "usage": null
}

So need to count logrpobs.content