Move from `setup.py` to `pyproject.toml`

[BenjaminRodenberg]

pyproject.toml is the current standard for providing metadata and dependency information. Requiring setuptools>=61 (#207) is a step into this direction. See also https://setuptools.pypa.io/en/latest/userguide/pyproject_config.html.

[fsimonis]

https://hatch.pypa.io/latest/intro/#existing-project
This can convert the setup.py to pyproject.toml