Function simulate_ei 

pub fn simulate_ei(
    n_exc: usize,
    n_inh: usize,
    w_ee: f64,
    w_ei: f64,
    w_ie: f64,
    w_ii: f64,
    p_conn: f64,
    ext_rate: f64,
    duration: f64,
    dt: f64,
    seed: u64,
) -> EIResult

Run a complete E-I balanced LIF network simulation.

All computation happens in Rust — connectivity build, Poisson input, Euler integration, spike detection, rate binning.