Fix optional logprobs field in ResponseTextDeltaEvent model

[ygbingo]

• I understand that this repository is auto-generated and my pull request may not be merged

Changes being requested

This pull request fixes a bug in the ResponseTextDeltaEvent model where the logprobs field is not always present in actual API responses, causing validation errors when parsing streamed events.

Specific change:

Before:

logprobs: List[Logprob]

After:

logprobs: Optional[List[Logprob]] = None

This makes the field optional and avoids ValidationError when logprobs is missing or explicitly null, which aligns with the actual OpenAI API behavior.

Additional context & links

• Related issue: [#2489](Validation error for ResponseTextDeltaEvent after updating to 1.97.1 #2489)
• This fix ensures compatibility with streamed response events that may omit logprobs.
• While this repository is auto-generated and this PR may not be merged, I hope this change can be reflected in the next SDK generation or help others encountering the same issue.