Function julia_escape 

pub fn julia_escape(
    z_init: Complex,
    c: Complex,
    max_iter: u32,
) -> (u32, Complex, Complex)

Pure evaluation loop optimised for Julia Sets.

Iterates z(n+1) = z(n)^2 + c with simultaneous derivative tracking dz. Returns (iteration_count, final_z, final_dz).