API: preprocessing.transformations

skyulf.preprocessing.transformations

Transformation nodes (PowerTransformer / SimpleTransformation / GeneralTransformation).

Per-engine apply paths are split into _apply_polars / _apply_pandas static helpers and dispatched via apply_dual_engine. The per-method expression builders for the simple and general transformations live in module-level dispatch dicts (_POLARS_OPS / _PANDAS_OPS) so each helper stays at low CCN.