Use black to format Python files

Black is a popular Python code formatter. By using it, contributors
don't need to think about the project's styles preferences and avoids
the need for hand-formatting. Instead, let the tool handle it. This can
help smooth the review process.

Updated existing tools to follow the integration docs:
https://black.readthedocs.io/en/stable/guides/using_black_with_other_tools.html

For more details, see the project:
https://github.com/psf/black