WIP: update old code: CI, python version, pre-commit and unittests

[jonas-eschle]

This repo has a few modernizations outstanding, here we do the most important ones to upgrade it to modern Python and make sure the unittests run.

Amongst the changes are:

• Upgrade to Python 3.10, drop 2.7
• Add more pre-commit checks, black formatting
• Update unittests, refactor helpers and replace "faulty" ones (?)

TODO:

• Unexpected result of logical operators pydata/numexpr#408, as some logical operators give unexpected results. Seemingly, the cast to booleans is not explicitly possible currently (will be in NE3). This raises the question of changing to sympy maybe?
• Some functions differ numerically in ROOT and numexpr. why?