Module input_standardization 

Per-axis input standardization and length-scale compensation helpers for the spatial smooth arm.

Pure numeric helpers relocated verbatim from smooth.rs (issue #780 decomposition): per-column variance scales, in-place standardization, the geometric-mean scale, and the kernel length-scale compensation maps that keep the Matérn/Duchon/thin-plate range in original coordinates after standardization. No behavior change — bodies are byte-identical and the parent re-imports each name so every call site is unchanged.

Functions

apply_input_standardization

Apply per-column standardization to a data matrix using precomputed scales.

compensate_length_scale_for_standardization

compensate_optional_length_scale_for_standardization

compute_spatial_input_scales

Compute per-column standard deviations for spatial inputs.