Function spectral_blend_emf 

pub fn spectral_blend_emf(
    alpha_a: f32,
    mu_a: f32,
    sigma_a: f32,
    alpha_b: f32,
    mu_b: f32,
    sigma_b: f32,
    t: f32,
) -> Xyz

Blend two EMF payloads in spectral space and return the resulting XYZ.