\brief A class for uniquely labelling and comparing PcodeOps Different PcodeOps generated by a single machine instruction can only be labelled with a single Address. But PcodeOps must be distinguishable and compared for execution order. A SeqNum extends the address for a PcodeOp to include: - A fixed \e time field, which is set at the time the PcodeOp is created. The \e time field guarantees a un