feat: usage struct add CompletionTokensDetails

[liushuangls]

referenced document: https://platform.openai.com/docs/api-reference/chat/object#chat/object-usage

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.03%. Comparing base (774fc9d) to head (e57b5ea).
Report is 57 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #863      +/-   ##
==========================================
+ Coverage   98.46%   99.03%   +0.57%     
==========================================
  Files          24       26       +2     
  Lines        1364     1454      +90     
==========================================
+ Hits         1343     1440      +97     
+ Misses         15        8       -7     
  Partials        6        6              

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[sashabaranov]

Thank you!