Add black pre-commit hook

[tjstavenger-pnnl]

The https://github.com/C2QA/bosonic-qiskit/blob/main/.github/workflows/python-package.yml workflow runs flake8 but doesn't actually change anything (developers have to check the build results and apply the suggestions manually).

Run black as a pre-commit hook so any new code is formatted.

Run black on the existing code so it gets formatted. PR #119 ran black too, so #120 may do this for us.

[tjstavenger-pnnl]

As pre-commit hooks are unique to each cloned repo, we may need to use a tool like https://pypi.org/project/pre-commit/ to help out.