Function cg_solve_chisep 

fn cg_solve_chisep(
    ws: &mut ChiSepWorkspace,
    d_kernel: &[f32],
    mx: &[f32],
    my: &[f32],
    mz: &[f32],
    vr_pos: &[f32],
    vr_neg: &[f32],
    vr_sum: &[f32],
    lambda_para: f32,
    lambda_dia: f32,
    lambda_sum: f32,
    lambda_cpl: f32,
    dr_p: f32,
    dr_q: f32,
    mask: &[u8],
    b: &[f32],
    x: &mut [f32],
    tol: f32,
    max_iter: usize,
)

CG solver for the doubled chi-sep system.