PCCD: check sd/sd2/refsd input in overlap and derivative functions

### Describe the task or issue:

- Crosscheck mention of m=sd/sd1/sd2 in slater.occ_indices(m) or slater.sign_excite(m)
- Move tmp_olp out of `_olp` and `_olp_deriv`
- Move `_olp` or `_olp_deriv` functionality inside `get_overlap` and `get_overlap_deriv` 