Disabled binarization strategy (placeholder).
binarize_disabled.RdPlaceholder binarizer for specs where binarization never fires —
notably regression, where `grouping_by_cutpoint()` always produces
a 2-group partition at each node. Selecting binarize_disabled()
documents that intent explicitly; if binarization is ever invoked at
runtime with this strategy configured, training aborts with a clear
error rather than silently passing through. Default for regression
specs.