ci: Remove volatile metadata from generated models header

[vdusek]

Summary

• Disable timestamp and filename in the datamodel-codegen header via pyproject.toml config
• Prevents spurious PRs when the OpenAPI spec hasn't changed but regeneration produces a diff due to volatile metadata (timestamp, source URL).

Test plan

• Regenerated models locally — header is now a single static line # generated by datamodel-codegen
• CI passes

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.24%. Comparing base (8a0e8e1) to head (67ddd05).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #718      +/-   ##
==========================================
- Coverage   95.34%   95.24%   -0.11%     
==========================================
  Files          45       45              
  Lines        4812     4812              
==========================================
- Hits         4588     4583       -5     
- Misses        224      229       +5     

Flag	Coverage Δ
integration	95.24% <ø> (-0.11%)	⬇️

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