Both packages had tests/__init__.py, creating competing `tests`
packages under --import-mode=importlib. Remove both __init__.py files
and change github-app imports from `from tests.helpers` to
`from helpers` via sys.path insertion in conftest.py.
* Fix mypy errors and apply ruff formatting across packages
Fix ast.FunctionDef calls missing type_params for Python 3.12+,
correct type: ignore error codes in _comparator and _plugin, and
run ruff format on all package source and test files.
* Switch CI to prek for lint/typecheck checks
Use j178/prek-action for consistent lint+typecheck (ruff check,
ruff format, interrogate, mypy) matching local pre-commit config.
Keep test as a separate parallel job for test-env support.
