Function spherical_degree 

pub(crate) fn spherical_degree(
    l: i32,
    orders: RangeInclusive<i32>,
    k: Complex,
    lattice: &BlochLattice,
    shift: [f64; 3],
    eta: Complex,
) -> Result<Vec<Complex>>

Consecutive orders of one spherical degree, sharing their real-space radial integrals while retaining each harmonic’s convergence policy.