Struct std::FBiquad

struct FBiquad {
    Fixed b0;
    Fixed b1;
    Fixed b2;
    Fixed a1;
    Fixed a2;
    Fixed z1;
    Fixed z2;
}

Q8.24 fixed-point biquad: coefficients are designed in double precision via the designers above, then quantized once with FBiquad::from — the same design-time-float/runtime-fixed split as the rest of std/dsp.