Function ion_plasma_angular_frequency 

pub fn ion_plasma_angular_frequency(
    ion_number_density: f64,
    ion_charge_state: f64,
    ion_mass: f64,
) -> Option<f64>

Computes the ion plasma angular frequency.

Formula: ω_pi = sqrt(n_i (Z e)^2 / (ε0 m_i))