MPI distribute to_array (Aka: Improve exact sampling)

Created by: PhilipVinc

This is another patch i am bored of carrying in my branches. It's been field tested for a while now.

It distributes to_array() across several MPI ranks by splitting the hilbert space in chunks. mpi4jax does not support MPI.Allgatherv and won't in the near future so the implemnetation is a bit more complicated than what could be.

This speeds up enourmously ExactSampler under MPI