Function py_fitzhugh_nagumo_simulate 

pub(crate) fn py_fitzhugh_nagumo_simulate<'py>(
    py: Python<'py>,
    v0: f64,
    w0: f64,
    a: f64,
    b: f64,
    epsilon: f64,
    dt: f64,
    v_threshold: f64,
    n_steps: usize,
    current: f64,
) -> (Bound<'py, PyArray1<f64>>, i64, f64, f64)

Parity contract with sc_neurocore.neurons.models.fitzhugh_nagumo.FitzHughNagumoNeuron.simulate: for the same parameters and constant input the returned v trace, upward- crossing spike count, and final (v, w) state are bit-identical to the Python RK4 reference (the right-hand side is exact arithmetic — a cube v.powi(3) = v*v*v, additions and multiplications, no transcendental functions — and a two-dimensional flow cannot be chaotic).