Format code

[kurtmckee]

This PR introduces black and isort as pre-commit hooks.

For now, the project's generated files are excluded from black's reformatting instead of making the generated output match.

Please let me know if additional changes are needed.

[!NOTE]

If this merges, I strongly recommend enabling pre-commit.ci for this project so that incoming PRs are automatically subjected to linting and reformatting.

In addition, enabling pre-commit.ci will cause the service to submit PRs on a quarterly basis (if needed) to update the hook versions in .pre-commit-config.yaml.

Closes #157