Function rc_lowpass_impulse_response 

pub fn rc_lowpass_impulse_response(
    r_ohms: f64,
    c_farads: f64,
    sample_rate: f64,
    n_samples: usize,
) -> Vec<f64>

First-order RC lowpass filter impulse response.

The continuous-time impulse response is: h(t) = (1/τ) * exp(-t/τ) for t ≥ 0 where τ = RC.

For a digital system, we sample this and normalize to get the discrete impulse response that, when convolved with input, gives the lowpass-filtered output.