make format command

[mshafer-NI]

We want a format command.

This format command supports:

• no args (formats)
• --diff prints the diff it would do
• --check sys.exits if changes would be made

To accomplish this:

• switch entirely to using isort and removing our own import sorting implementation.
• bring in better-diff to make output that adds on top of the standard unified diff (notably, highlights changes in trailing whitespace or lines)

Note: to make the output of running nps format --diff consistent, calls to black had -q added to "1 file formatted" output (will also impact fix).

[github-actions]

Thank you for contributing! 👋