Make EventHandlers run on certain conditions.

[SEGVeenstra]

This idea is to prevent writing unnecessary and repetitive code.

Sometimes you don't want to execute the handler in a specific state.
For example you don't want to load items when the state is not Authenticated.

We could think about separating the condition from the rest of the logic.

maybe a separate function:

class LogoutEventHandler extends EventHandler<AppState, LogoutEvent> {

  @override
  bool shouldRun(AppState state) => state is AuthenticatedAppState; // you can only logout when you're logged in.

  @override
  FutureOr<void> call(
    LoadTodosEvent event,
    StateGetter<AppState> getState,
    StateSetter<AppState> setState,
  ) async {
   final authenticatedState = getState() as AuthenticatedAppState; // we can safely do this because shouldRun prevents this.
   // do everything to logout
    
  }

}