Function magnetic_flux_density_from_flux 

pub fn magnetic_flux_density_from_flux(
    flux: f64,
    area: f64,
    angle_radians: f64,
) -> Option<f64>

Computes magnetic flux density from magnetic flux, area, and orientation.

Formula: B = Φ / (A * cos(theta))

Returns None when area is less than or equal to zero, when cos(theta) is zero or effectively zero, when any input is not finite, or when the computed result is not finite.