tox.ini: Revise and extend format checks
Use both flake8 and black for linting Python files.
Add 'reformat' environment to use black for reformatting.
Ran reformat to make existing Python files compliant.
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Use both flake8 and black for linting Python files.
Add 'reformat' environment to use black for reformatting.
Ran reformat to make existing Python files compliant.