This implements [Algorithm 0 of RFC 8554](https://datatracker.ietf.org/doc/html/rfc8554#section-4.2) with a pseudorandom process for generating `x`. Please document this process.    x[i] = H(I || u32str(q) || u16str(i) || FF || seed)    This is the process described in [RFC 8554 appendix A](https://datatracker.ietf.org/doc/html/rfc8554#appendix-A).