Remove MO coefficient dependence from `occupations_from_pyscf_mol`

[berquist]

pymolresponse/pymolresponse/interfaces/pyscf/utils.py

Lines 12 to 16 in e3a7875

	def occupations_from_pyscf_mol(mol: pyscf.gto.Mole, C: DirtyMocoeffs) -> "Occupations":
	norb = fix_mocoeffs_shape(C).shape[-1]
	nocc_a, nocc_b = mol.nelec
	nvirt_a, nvirt_b = norb - nocc_a, norb - nocc_b
	return nocc_a, nvirt_a, nocc_b, nvirt_b

It runs fix_mocoeffs_shape on the coefficients and then doesn't even return them, which is wasteful.

1. In the short term, figure out how to get norb from mol.
2. In the long term, maybe there should be a class that handles MO coefficients, MO energies, occupations, and the program's molecule/wavefunction/etc. object together. The functional composition right now is nice but I keep repeating the same things over and over again.