Replace legacy setup.py packaging with modern pyproject.toml (PEP 517/518/621).
Version is dynamically resolved via setuptools attr: directive from rips/_version.py,
which CMake generates.
Consolidate requirements.txt, dev-requirements.txt, and build-requirements.txt
into pyproject.toml dependencies and [dev] optional-dependencies.
Consolidate rips/mypy.ini into [tool.mypy] section of pyproject.toml.
Update GitHub Actions workflow and CMakeLists.txt accordingly.
