Meta data to rng functions

[pvdz]

We shouldn't use bare rng functions inside the project but instead an object that contains the meta data so we can reconstruct the function if needed.

Basically right now we accept a rng (like Math.random, or something more reproducable for prod, or something fixed for tests) which is just a function. But once we have it we can't really trace back how it was created. This makes it harder to generate the code to reproduce a particular test case.

Something like this would solve it:

{
  _class: 'special_rng',
  _params: 'fcxfds9fdsfua9uf98ds',
  roll: function(){ ... },
}

Then we can figure out what created the function through _class, recreate it through the _params property, and just call it through rng.roll().