Function mu_from_heating

pub fn mu_from_heating<F>(dq_dz: F, z_min: f64, z_max: f64, n_z: usize) -> f64
where
    F: Fn(f64) -> f64,

Extract μ parameter from the Green’s function approximation.

μ = (3/κ_c) ∫ J_bb*(z) · J_μ(z) · d(Δρ/ρ)/dz dz

Calls mu_y_from_heating internally and returns the μ component. For simultaneous μ and y, use mu_y_from_heating directly.