Set up automated code health checks

To ensure this project is welcoming to contributions from the general public, automated code health tooling should be set up to enforce code style and detect antipatterns.

Completion criteria

• PEP 484 type hints have been added to the codebase
• PEP 526 variable annotations have been added to the codebase
• Continuous Integration automatically runs the following tools on each Pull Request:
  • black
  • isort
  • flake8
  • mypy
  • pytest