Function std::bilinear_nth_order

int bilinear_nth_order(
    []const double B,
    []const double A,
    double fs,
    []double bOut,
    []double aOut,
)

B, A: order+1 analog (s-domain) coefficients each, ascending powers of s (B[0]/A[0] is the constant term, B[order]/A[order] is the s^order term). bOut, aOut: order+1 digital (z-domain) coefficients each, written in the negative-power-of-z convention (bOut[0]/aOut[0] is the z^0 term, bOut[order]/aOut[order] is the z^-order term), normalized so aOut[0] = 1 — the same normalization Biquad::bilinear's a0-divide-out already uses, and what IirFilter expects.