Function cg_solve_tfi 

fn cg_solve_tfi<F>(
    ws: &mut MediWorkspace,
    precond: &[f32],
    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 for the preconditioned TFI operator.

Solves A_tfi(y) = b where A_tfi(dy) = P ⊙ A_medi(P ⊙ dy). The MEDI operator itself is reused unchanged.