> ... move the `preRestart` and `postRestart` implementations to `Processor` and make them `final`.

Making them final limits composition with existing traits. For example making `postStop()` final on `Processor` prevents mixing in the FSM trait. I propose to leave the `preStart`, `postStop`, `preRestart` and `postRestart` non-final but still recommend overriding `preStartProcessor`, `postStopProcessor`, `preRestartProcessor` and `postRestartProcessor` if possible.