Avoid unnecessary imports and computations at load time + refactoring / linting

• remove "import everything" from code (on-going effort)
• evaluating the qnms lazily
• faster dynamics interpolation + tests

Other:

• isort/cython-lint/flake8 configuration in pyproject
• upgrading pre-commits to use isort, flake8 and cython-lint checks
• CI and tox improvements
• blacking/isorting/linting files

Fixes #20 (closed) and #17 (closed)

note there is a lot of changes but those are mostly due to reformating of the files. Best viewed in GitLab as side-by-side diffs.