Refine type hint for solve_fermion()'s 'spin_sq` argument

[haimeng-zhang]

In solve_fermion(), the type hint for spin_sq parameter should be float instead of int. This parameter represents spin squared expectation value of the target ground state S^2 = s(s+1), where s is the spin quantum number taking values of $\frac{n}{2}$ (n being an integer). Therefore, spin_sq should accept float values.

[caleb-johnson]

In solve_fermion(), the type hint for spin_sq parameter should be float instead of int. This parameter represents spin squared expectation value of the target ground state S^2 = s(s+1), where s is the spin quantum number taking values of n 2 (n being an integer). Therefore, spin_sq should accept float values.

Thank you for submitting this! You're right, this should be a float (or np.number). The only type hint I could find for this in pyscf was here in fix_spin(), and it seems to be a np.number. I think it's fine if we just use float.

It turns out Dice expects spin input as an int. I also opened an issue to correct the explanations around spin for that package as well.