0.16.1

Faster fits at identical output: internal model selection no longer recomputes preprocessing. The variant auditions, the cross-feature candidate, and the winner refit inside one fit previously each reran the full preprocessing pipeline (target encoding, quantile borders, binning); they now share it. Models are bit-identical to 0.16.0 (verified by numerical-identity goldens and exact prediction ties on all 73 benchmark datasets). Biggest on categorical-heavy data (17-32% faster single-model fits measured there); bagged ensembles save it in every member. See CHANGELOG.md.