Add controlled system state space size as statistics option

Currently, data-based synthesis can calculate an estimation or precise state space size of the controlled system, where the latter is obtained if the forward reachability is turned on. But this information is only presented if data-based synthesis is run in debug mode.

For use-case papers, we often report the state space size of the uncontrolled and controlled system. Therefore, I think it would fit better if this becomes an option under statistics and is being decoupled from the mode.