Move to hatch and pyproject.toml

[mikealfare]

We are moving to a monorepo that uses pyproject.toml and hatch. This requires a series of migrations, including this one. This PR inclues:

• update from setup.py/dev-requirements.txt to pyproject.toml/hatch.toml
• move tool config (e.g. mypy and pytest) into pyproject.toml
• update workflows regarding these moves
• delete configs that no longer apply (e.g. tox.ini, pytest.ini, etc.)

[github-actions]

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