fix moonshot usage compatible problem

[rinfx]

moonshot在返回最后一个chunk的时候，usage部分与openai不一致：

moonshot示例：

{
    "id": "chatcmpl-67500eb0c51af667d5968f74",
    "object": "chat.completion.chunk",
    "created": 1733299889,
    "model": "moonshot-v1-8k",
    "choices": [
        {
            "index": 0,
            "delta": {},
            "finish_reason": "stop",
            "usage": {
                "prompt_tokens": 10,
                "completion_tokens": 79,
                "total_tokens": 89
            }
        }
    ],
    "system_fingerprint": "fpv0_c26222aa"
}

openai示例：

{
    "id": "chatcmpl-675047e668e5d6e235622193",
    "object": "chat.completion.chunk",
    "created": 1733314534,
    "model": "moonshot-v1-8k",
    "choices": [
        {
            "index": 0,
            "delta": {},
            "finish_reason": "stop"
        }
    ],
    "system_fingerprint": "fpv0_80e0c0a3",
    "usage": {
        "prompt_tokens": 10,
        "completion_tokens": 27,
        "total_tokens": 37
    }
}

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 43.50%. Comparing base (ef31e09) to head (3c6f377).
Report is 216 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1568      +/-   ##
==========================================
+ Coverage   35.91%   43.50%   +7.59%     
==========================================
  Files          69       76       +7     
  Lines       11576    12325     +749     
==========================================
+ Hits         4157     5362    +1205     
+ Misses       7104     6627     -477     
- Partials      315      336      +21     

see 69 files with indirect coverage changes

[johnlanni]

LGTM