API: preprocessing.drop_and_missing

skyulf.preprocessing.drop_and_missing

Drop / missing-value nodes (Deduplicate / DropMissingColumns / DropMissingRows / MissingIndicator).

Appliers route through :func:apply_dual_engine; fits that need engine-divergent math (column null-percentage scans) route through :func:fit_dual_engine. The two splitter-friendly nodes (Deduplicate, DropMissingRows) require a keep-indices y-sync — handled by :func:_polars_filter_y_by_kept_indices.