update azero_pruning_cutoff during arity zero in the NON cfg.inv_candidates == 1 case as well too

[mlb2251]

Right now we only do the inv_candidates==1 case since that's such a major focus of this work and we never really look a cfg.inv_candidates > 1, however note that due to how expensive inverse_argument_capture() the azero_pruning_cutoff is actually rather important to update along the way instead of just at the end, so we should really be updating this along the way too. Just do the usual pushing to a donelist and calling .update(), should be simple!