Use a separate rng for framework internal operations to improve robustness

[ghost]

Some libraries like sympy manipulate the standard RNG in unpredictable ways. By using an internal RNG we can prevent such libraries from making purely framework based operations like selecting choices or permutations non-deterministic.

[brando90]

Dan maybe we can add units tests to this and the general framework to make sure it works as we expect? but besides that it looks good to me