performs n_folds-CV but with only input-preprocessing the test set. No calibration model is trained and evaluated in this method. The predicted values are partitioned into n subsets. The training set is constructed on (n-1) subsets; the remaining set is used for testing. Since no calibration model is used in this method, the test set predictions are only input-preprocessed (either scaled or transformed, depending on input). All test set predictions are merged and used to compute error metrics for the input-preprocessing methods.