//! Layer 2: Math
//!
//! This layer provides pure mathematical functions used throughout LOESS:
//! - Kernel functions for distance-based weighting
//! - Robust statistics (MAD/MAR)
// Kernel (weight) functions for distance-based weighting.
// Default values for math module types.
// Robust scale estimation (MAR/MAD).
// Boundary padding utilities.
// Distance metrics for nD LOESS.
// nD neighborhood search (KD-Tree implementation).
// Linear algebra backend abstraction.
// Hat matrix and delta parameter computation.