Streaming Chat Completion via OpenAI API should support stream option to include Usage

[odrobnik]

In streaming mode the OpenAI chat completion has a new parameter to include Usage information after the Chunks. You just add a { "include_usage": true } to the request.

Then the final chunks will look like this:

...
data: {"id":"chatcmpl-9P4UJf7DEdyXVro2VOMRMT9qKR0bC","object":"chat.completion.chunk","created":1715762479,"model":"gpt-3.5-turbo-0125","system_fingerprint":null,"choices":[{"index":1,"delta":{},"logprobs":null,"finish_reason":"stop"}],"usage":null}
data: {"id":"chatcmpl-9P4UJf7DEdyXVro2VOMRMT9qKR0bC","object":"chat.completion.chunk","created":1715762479,"model":"gpt-3.5-turbo-0125","system_fingerprint":null,"choices":[{"index":2,"delta":{},"logprobs":null,"finish_reason":"stop"}],"usage":null}
data: {"id":"chatcmpl-9P4UJf7DEdyXVro2VOMRMT9qKR0bC","object":"chat.completion.chunk","created":1715762479,"model":"gpt-3.5-turbo-0125","system_fingerprint":null,"choices":[],"usage":{"prompt_tokens":24,"completion_tokens":58,"total_tokens":82}}
data: [DONE]

The final chunk contains no choices, but a usage:

"usage":{"prompt_tokens":24,"completion_tokens":58,"total_tokens":82}

This usage is over all the generations from this stream.