API: preprocessing.feature_generation
skyulf.preprocessing.feature_generation
Feature-generation nodes (PolynomialFeatures + FeatureGeneration math).
Per-engine apply paths are split into small handlers and dispatched via
:func:apply_dual_engine. The per-operation logic (arithmetic /
ratio / similarity / datetime_extract) lives in module-level
helpers indexed by _FEATGEN_OPS_POLARS / _FEATGEN_OPS_PANDAS.
Calculator fit paths are sklearn-bound, so they use :func:to_pandas
once at the top instead of going through fit_dual_engine.