Fuzzing

[Adzz]

Just an early thought but

It would be great if you could easily generate either valid schemas, or valid input data that could be consumed by a schema.
Even better if this is random in some way.

So one way we could do that is add another (optional) callback to the cast_fn that let you define generators for input to the cast fns.

If that is implemented then you could easily generate example data from it without needing factories or anything like that.