When performing reads/writes from multiple threads, CIWBMasterAccessor does not provide any
protection, leading to data from one request being delivered to another.

By replacing the data queues with SV mailboxes, we ensure that only one thread can access the
mailbox at any given time. Furthermore, we add a SV event in wb_cycle_t, which is used to notify
the readm()/writem() tasks that their transfer is complete, to avoid getting the result of the
wrong transfer.