Set composition

It's possible to compose Sets via the flatMap method. This allows to randomly configure other Sets.

One of the main features of Sets is that they can shrink the generated values. This helps find the minimum values that make a test fail.

But in the case of the use of Set::flatMap() the value generated to configure another Set escape the control of the parent Set.

In order for this value to still be shrunk, BlackBox needs to track every use of it. To achieve this the value is wrapped in a Seed monad. This monad records every transformation (the callables passed to map and flatMap) and apply them when unwrapping the value. This way we can shrink the initial value and then re-apply the transformations.

If a user calls Seed::unwrap() to directly manipulate the value then BlackBox can no longer shrink this value.

While this design allows to maintain every feature across all possible compositions it introduces a complexity problem in the shrinking design.