Add `jumpy.random.Generator`

Jumpy's random functions are a bit weird for numpy as it uses a `np.array` as the key but needs to convert this to the `RandomState` for each function call.
Imo, as Gymnasium and other projects use `np.random.Generator` then it makes it difficult to easily change to using jumpy rather than numpy.

Therefore, the proposal is to create a `jp.random.Generator` object that is equivalent to `np.random.Generator` for numpy and for jumpy, behind the scenes we store the key and split the `prng` and return the results.

To consider is if the object inherits from `np.random.Generator` with functions being overrides with a check if numpy or jax is used.