Move infrastructure from tox/pytest to something more robust

[MateusAraujoBorges]

We need to improve the infrastructure to allow for longer fuzzing periods (i.e. days). Here are some alternatives that we might consider (or use as inspiration):

• https://github.com/MozillaSecurity/FuzzManager - probably too heavy and full of features to use directly.
• https://github.com/renatahodovan/fuzzinator - written in python. Might be worth a look