Statechart transition with trigger of type rate. Such transition is executed with
the timeout distributed exponentially with the parameter rate (counted from the
moment the statechart came to the transition's source state), i.e. if
the rate is 5, the timeout will on average be 1/5 of thr time unit. If the rate
changes dynamically, the timeout gets re-evaluated; such changes may
only be noticed by TransitionRate if onChange() is called for the agent.
If the guard appears to be false when the transition is about to execute,
it is not taken and becomes inactive until the rate changes. Memory: sizeof(Transition) + 8 = 30 bytes