Function pressure_change_from_bulk_modulus 

pub fn pressure_change_from_bulk_modulus(
    bulk_modulus: f64,
    volume_strain: f64,
) -> Option<f64>

Computes pressure change from bulk modulus and volumetric strain.

Formula: ΔP = -K * volume_strain.

Returns None when bulk_modulus is negative or when any input or result is not finite.