chore: export more types

[stainless-app]

No description provided.

[PHclaw]

For the streaming response type inconsistency:

When using stream=True, the choices[0].delta.content can be None on the first and last chunks. Fix:

async def stream_chat(client, messages):
    response = await client.chat.completions.create(
        model='gpt-4',
        messages=messages,
        stream=True
    )
    collected = []
    async for chunk in response:
        delta = chunk.choices[0].delta
        if delta.content is not None:
            collected.append(delta.content)
            yield delta.content
    return ''.join(collected)