Returns a list of scalar metrics present on the fit. No quantities are
recomputed; absent fields appear as NA_real_. LOO p-value uses 2x2
Fisher exact when stored and available (p_status = "computed"); if
the value is absent or NA the status is "not_computed" with an
explicit reason. Multiclass/polychotomous LOO always returns
p_status = "not_computed".
Usage
oda_metrics(fit, split = c("train", "loo"))