Function ridge_cv 

pub fn ridge_cv(
    x: Vec<f64>,
    n_obs: usize,
    n_vars: usize,
    time: Vec<f64>,
    status: Vec<i32>,
    theta_grid: Option<Vec<f64>>,
    n_folds: Option<usize>,
) -> PyResult<(f64, Vec<f64>)>

Select optimal ridge penalty using cross-validation