test: Set up pre-commit hooks and fix quality nits

[giovannicimolin]

This PR implements:

• A pre-commit hook that runs isort and flake8
• Code coverage reports and codecov WIP

[giovannicimolin]

Relates to #304.

[codecov]

Codecov Report

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@@            Coverage Diff             @@
##             develop     #308   +/-   ##
==========================================
  Coverage           ?   90.30%           
==========================================
  Files              ?        9           
  Lines              ?      227           
  Branches           ?       35           
==========================================
  Hits               ?      205           
  Misses             ?       19           
  Partials           ?        3           

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[giovannicimolin]

It worked! Still needs some improvements. I'll do them on a follow-up ticket. :)