Function spectral_integral

pub fn spectral_integral(
    n: i32,
    x_min: f64,
    x_max: f64,
    num_points: usize,
) -> f64

Numerical integral of x^n * n_pl(x) over [0, x_max] using the trapezoidal rule on a logarithmic grid. Used for validation against analytic G_n values.