Function process_jacobian 

pub fn process_jacobian(
    jacobian: &SparseColMat<usize, f64>,
    jacobi_scaling: &mut Option<SparseColMat<usize, f64>>,
    iteration: usize,
) -> Result<SparseColMat<usize, f64>, OptimizerError>

Process Jacobian by applying Jacobi scaling (created on first iteration).

On iteration == 0, creates the scaling matrix and stores it. On subsequent iterations, reuses the cached scaling.