Function cg_solve_medi 

fn cg_solve_medi<F>(
    ws: &mut MediWorkspace,
    w: &[Complex32],
    d_kernel: &[f32],
    mx: &[f32],
    my: &[f32],
    mz: &[f32],
    vr: &[f32],
    lambda: f32,
    b: &[f32],
    x: &mut [f32],
    tol: f32,
    max_iter: usize,
    progress_callback: F,
)
where
    F: FnMut(usize, usize),

Conjugate gradient solver with buffer reuse Solves Ax = b where A is the MEDI operator

The optional progress callback receives (cg_iter, max_iter) for each CG iteration. Uses per-direction gradient masks (mx, my, mz) matching MATLAB MEDI.