Add pre-commit configuration and use it in CI

[timokau]

Description

Run black pre-commit and on CI.

Motivation and Context

As a follow up to #78, we should run black locally pre-commit and verify that this was done on CI. Otherwise the formatting would slowly shift away from the black standard again.

How Has This Been Tested?

By creating this PR.

Does this close/impact existing issues?

#78

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.

[timokau]

Looks like this is working. A disadvantage is that the pre-commit hook is run 4 times, once for each listed environment. The same issue already exists with the docbuild though, where it is probably more relevant (running black is fast enough). This brings us back to #66 -- we probably should figure out a better way to parallelize the tests long-term.

But for now I think this is ready for review.

[coveralls]

Pull Request Test Coverage Report for Build 742

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-9.05%) to 49.786%

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Totals
Change from base Build 740:	-9.05%
Covered Lines:	3719
Relevant Lines:	7470

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💛 - Coveralls