0.5.0

• Restructured the code, splitting the single protego.py file into
  multiple modules. The public API remains the same but some internal names
  may now be available at different import paths.
• Added type hints and py.typed.
• Added official support for PyPy 3.11.
• Switched the build backend from setuptools to hatchling.
• Switched from setup.py to pyproject.toml.
• CI fixes and improvements.