ksp: fix Model declaration

src/utility/shortestPaths.cpp

@@ -1,6 +1,10 @@
 #include "shortestPaths.h"
 #include "storm/utility/shortestPaths.h"
 
+// only forward declaring Model leads to pybind compilation error
+// this may be avoidable. but including certainly works.
+#include "storm/models/sparse/Model.h"
+
 #include <sstream>
 #include <string>