Function hohmann_transfer_semi_major_axis 

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

Computes the semi-major axis of a Hohmann transfer ellipse.

Formula: a_transfer = (r1 + r2) / 2

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