Function transverse_strain_from_poisson_ratio 

pub fn transverse_strain_from_poisson_ratio(
    poisson_ratio: f64,
    axial_strain: f64,
) -> Option<f64>

Computes transverse strain from Poisson’s ratio and axial strain.

Formula: ε_transverse = -ν * ε_axial.

Returns None when any input or result is not finite.