Description of the change

Black has recently been updated to a stable build. In this update spaces around power operators are removed automatically. I have reformatted the repository black . so that the CI code check is happy for future PR. The black version number in pre-commit-config.yaml has been bumped.

Closes #273.

Progress of the PR

• [n/a] Docstrings for all functions
• [n/a] Unit tests with pytest for all lines
• Clean code style by running black via pre-commit

For reviewers

• The PR title is short, concise, and will make sense 1 year later.
• New functions are imported in corresponding __init__.py.
• New features, API changes, and deprecations are mentioned in the
  unreleased section in CHANGELOG.rst.