//! Nonlinear, covariance, and linear least-squares APIs.
//!
//! # Status: Partial
//!
//! This permanent namespace has no callable API until a least-squares feature
//! is selected. Exact solver signatures remain at their compatibility paths.
/// Covariance estimation for nonlinear least-squares fits.
/// Linear least-squares fitting.
/// Nonlinear least-squares fitting.