fix: add ruff check to CI and fix all lint errors

[webjunkie]

Summary

CI was only running ruff format --check but never ruff check, allowing lint errors to accumulate undetected on master.

Problem

The code quality checks in CI only verified formatting:

- name: Check formatting with ruff
  run: |
      ruff format --check .

But never ran linting checks, so errors like unused imports, duplicate function names, and lambda expressions were merging undetected.

Changes

1. Add ruff check step to CI workflow
2. Fix all existing lint errors on master:
   • F401: Add explicit re-exports for public API types (InconclusiveMatchError as InconclusiveMatchError, etc.)
   • F811: Rename duplicate test_openai_reasoning_tokens to test_openai_reasoning_tokens_o4_mini
   • E731: Convert lambda to def function in test_middleware.py
   • Unused imports: Remove unused imports from client.py and test files (auto-fixed)

Testing

$ ruff check .
All checks passed!

Impact

Going forward, ruff check will run in CI and catch lint errors before they merge, maintaining code quality standards.

[greptile-apps]

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