Add postponed annotations to test modules and modernize one test helper annotation for Python 3.9-compatible collection.
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Co-authored-by: Codex <codex@openai.com>
* refactor: reorganize project structure and update module imports
* configure setuptools to use 'src' layout and adjust package discovery
* refactor: move tests to `tests` directory and update imports accordingly
* update lint and mypy configurations to align with `src` and `tests` structure
* update test imports to use corrected `tests.helpers` module path
* fix(pre_commit): 🎨 auto format pre-commit hooks
Jirka Borovec