Require tools to match states

[jwnys]

It often happens that we need to minimize the distance/maximize the overlap between a variational state and some fixed reference state. For example, in simulation of quantum devices, or in analyses like "https://onlinelibrary.wiley.com/doi/pdf/10.1002/pssb.202100172", or maybe also in time evolution (?).
It would be very useful to have a generic class, say "StateCompilation", which takes a reference state (can be an array, ExactState, or MCState), and a generic "loss_and_grad_fn", which takes the variational state and reference state as input.
This would allow us to e.g. create an infidelity, KL divergence, MSE, etc minimization with one driver class.

Apart from the driver, one also could use such measures/metrics/losses (especially infidelity) to compute excited states through orthogonalization.
@inailuig has many of the necessary ingredients already.
To my knowledge, such things do not exist yet in NetKet @PhilipVinc ?

[inailuig]

• supervised driver: https://github.com/inailuig/netket/commits/supervised
• fidelity optimization: https://github.com/inailuig/netket/commits/fidopt

both are working, but would need some polishing if we ever want to merge...