Function hohmann_transfer_time 

pub fn hohmann_transfer_time(
    mu: f64,
    radius_initial: f64,
    radius_final: f64,
) -> Option<f64>

Computes the transfer time for a Hohmann transfer.

Formula: t_transfer = π * sqrt(a_transfer³ / μ)

Returns None when mu is less than or equal to zero, when either radius is less than or equal to zero, or when the input or result is not finite.