feat: add model id on token usage

[dartpain]

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

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Project	Deployment	Actions	Updated (UTC)
nextra-docsgpt	Ready	Preview, Comment	May 28, 2026 6:29pm
oss-docsgpt	Ready	Preview, Comment	May 28, 2026 6:29pm

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.44%. Comparing base (9b8fe2d) to head (08c6867).
⚠️ Report is 50 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2507      +/-   ##
==========================================
- Coverage   91.34%   89.44%   -1.90%     
==========================================
  Files         248      288      +40     
  Lines       20709    25526    +4817     
==========================================
+ Hits        18916    22832    +3916     
- Misses       1793     2694     +901     

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