Function mu_y_from_heating

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

Compute both μ and y from an arbitrary energy release history in a single pass.

This is more efficient than calling mu_from_heating and y_from_heating separately, as it evaluates the visibility functions only once per z-step.

Returns (μ, y).