"save" and "restore" using explicit byte array

I think that the current implementation of "save" and "restore" (of the internal state of a RNG) does not gain anything from attempting to hide (using a marker interface) that the state is represented by a byte[] primitive array.

Moreover, hiding the concrete class (that implements the marker interface and Serializable) in the BaseProvider internal class is also needlessly complicated with no clear benefit.

I propose to replace the marker interface with a concrete class that wraps a byte[] field with a public accessor method.
As before, library users do not need to know how the actual state of a RNG is represented by this field, but can directly serialize the byte[] field returned by the getter.