public static Vec256 <T> ToCpuVec <T>(this BitString src, N256 n) where T : unmanaged => src.Pack().As <byte, T>().ToSpan256().ToCpuVec256();
public static BitVector4 FromBitString(BitString src) => new BitVector4(src.IsEmpty ? (byte)0 : src.Pack()[0]);
public static Vec128 <T> ToCpuVec <T>(this BitString src, N128 n) where T : unmanaged => src.Pack().As <byte, T>().ToSpan128().ToCpuVec128();