compatiable with openai sdk

[johnlanni]

Ⅰ. Describe what this PR did

before:

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data:{"id":"c73fe96b-2a20-976d-a2db-391cb3c8cbe6","choices":[],"created":1719386456,"model":"qwen-max","object":"chat.completion.chunk","usage":{"prompt_tokens":131,"completion_tokens":197,"total_tokens":328}}

after:

data:{"id":"c73fe96b-2a20-976d-a2db-391cb3c8cbe6","choices":[{"index":0,"delta":{},"finish_reason":"stop"}],"created":1719386456,"model":"qwen-max","object":"chat.completion.chunk","usage":{}}

data:{"id":"c73fe96b-2a20-976d-a2db-391cb3c8cbe6","choices":[{"index":0,"delta":{}}],"created":1719386456,"model":"qwen-max","object":"chat.completion.chunk","usage":{"prompt_tokens":131,"completion_tokens":197,"total_tokens":328}}

Ⅱ. Does this pull request fix one issue?

Ⅲ. Why don't you add test cases (unit test/integration test)?

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews