Function spike_field_coherence 

pub fn spike_field_coherence(
    binary_train: &[i32],
    lfp_signal: &[f64],
    dt: f64,
) -> (Vec<f64>, Vec<f64>)

Spike-field coherence (SFC).

Returns (coherence, freqs_hz). SFC = |S_xy|^2 / (S_xx * S_yy).