[Proposal] Migrate to fast-check

[dubzzz]

What? This Pull Request is mostly a proposal to migrate from jsverify to fast-check.

Why? jsverify's owner stopped the maintenance of the library more than a year ago. In addition, the last real commit to jsverify was on the 6th of September 2019.

Benefits of fast-check over jsverify

1. You don't need to define unmapping fuctions on your calls to map (smap in jsverify).
2. The arbitraries are able to find more bugs. For instance if you take a look into the updated tests you'll see that I had to calm down the generator of numbers because it was reporting issues if we used it fully.
3. There is a built-in way to handle commands. But I did not adapt the tests of LRUCache yet (they can definitely use the builder of commands provided by fast-check).
4. Maintained.