ot::MeshCoP::JoinerPskd::IsValid() const method

Indicates whether the PSKd if well-formed and valid. Per Thread specification, a Joining Device Credential is encoded as uppercase alphanumeric characters (base32-thread: 0-9, A-Z excluding I, O, Q, and Z for readability) with a minimum length of 6 such characters and a maximum length of 32 such characters.