test: Run the model generator in unit tests

[vdusek]

PR CI never runs poe generate-models. Only the nightly regeneration workflow does, so a datamodel-code-generator update that breaks generation can pass CI and automerge through Renovate. The first sign would be a failed nightly run.

The new unit test runs both codegen passes with the repo's [tool.datamodel-codegen] config on a small spec, then the post-processing script. It checks the result: docs_group decorators, the camelCase alias generator, AwareDatetime for date-time, enums turned into open Literal[...] | str aliases in _literals.py, and TypedDict pruning plus camelCase twins. It runs in under a second.

Same idea as apify/apify-client-js#1097.

✍️ Drafted by Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.30%. Comparing base (9be215b) to head (e418631).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1082   +/-   ##
=======================================
  Coverage   95.30%   95.30%           
=======================================
  Files          60       60           
  Lines        5753     5753           
=======================================
  Hits         5483     5483           
  Misses        270      270           

Flag	Coverage Δ
integration	91.41% <ø> (-0.13%)	⬇️
unit	87.74% <ø> (ø)

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