[TODO] Tweak output of pytest and tox in CI and locally

[webknjaz]

I'd like to implement verbose reruns on failure like in other projects I got, with better explicit configs and CI+tox+pytest integration. This is a task for me, I'm recording it, so I don't forget.

https://docs.pytest.org/en/stable/how-to/output.html#producing-a-detailed-summary-report