Update: maybe not such a good idea, because your _fit_mle_lbfgs covers several cases of loglike and score

Since this is mainly for optimization and doesn't affect other statistical results, I would define it in terms of the negative logliglihood `nloglike_and_score`   avoids the negation.

in statsmodels.base.model.GenericLikelihoodModel and subclasses, I used `nloglike`