Function verify_signed_answer 

pub fn verify_signed_answer(payload: &[u8]) -> Option<VerifiedQuestionAnswer>

Verify a persisted question_response payload.

Returns Some(record) if the signature checks out against the embedded public key (the caller is responsible for trusting that public key — see verify_signed_answer_pinned). Returns None if the payload is malformed, the hex fields don’t decode, or the signature doesn’t verify.