Hamiltonian(s) giving wrong results with different hilbert spaces

Created by: jwnys

The nk.operator._hamiltonians.py Hamiltonians take a Hilbert space as input. However, e.g. nk.operator.Ising is implemented specifically with nk.hilbert.Spin in mind. If you call it with nk.hilbert.Qubit, the results are incorrect, and no error or warning is thrown. Pauli matrices in the corresponding Hilbert spaces should be used, as I've done in nk.operator.PauliStrings.