Refactor: Move splitting logic to separate module and create additional interfaces #1783
Description
#1780 adds splitting method to the MetaSWAP models as well. The splitting methods contain quite some logic, so I think it is best to move them to
Furthermore, it is probably wise to create a SplittingPackage interface, just like we have one for RegriddingPackage. Right now we had to add a IPackageBase interface to allow splitting certain packages which were splittable, but not regriddable (mainly MeteoGrid), which was very confusing.