MPS machine in 3.0 using JAX

Created by: gcarleo

MPS machines are now written in C++ and at present there is no plan to port them into the pure-python netket 3.0.

I am pinging here @stavros11, in case he wanted to port them to numpy.

[Incidentally, this is a much easier task than writing the full class as it was done in C++, since it involves basically writing only the log_val(x) method and the der_log(x), using numpy objects. In other words, there is no look-up table logic and all the other complications that we used to have]