ChatCompletionsChunk

Streaming chunk for Chat Completions API.

This follows OpenAI's streaming response format for chat completions. Each chunk contains a delta with partial content.

Example streaming chunk:

{
"id": "chatcmpl-xxx",
"object": "chat.completion.chunk",
"created": 1234567890,
"model": "gpt-4",
"choices": [{
"index": 0,
"delta": {"content": "Hello"},
"finish_reason": null
}]
}

Tool call streaming chunk:

{
"id": "chatcmpl-xxx",
"object": "chat.completion.chunk",
"created": 1234567890,
"model": "gpt-4",
"choices": [{
"index": 0,
"delta": {
"tool_calls": [{
"index": 0,
"id": "call_abc",
"type": "function",
"function": {"name": "get_weather", "arguments": "{...}"}
}]
},
"finish_reason": null
}]
}