Give the Hartree-Fock state of jellium.

grid (Grid): The discretization to use. n_electrons (int): Number of electrons in the system. spinless (bool): Whether to use the spinless model or not. plane_wave (bool): Whether to return the Hartree-Fock state in the plane wave (True) or dual basis (False).

The jellium model is built up by filling the lowest-energy single-particle states in the plane-wave Hamiltonian until n_electrons states are filled.