Function visibility_j_t

pub fn visibility_j_t(z: f64) -> f64

Temperature shift branching: fraction of energy going into temperature shift.

J_T(z) = 1 − J_bb*(z)

Following Chluba (2013), the temperature-shift coefficient is (1 − J_bb*), which captures the fraction of energy fully thermalized into a blackbody. This is the standard convention used in the literature.