Use ArrayStorage for boundary nodes to optimize MLD

For the MLD algorithm we can partition the NodeID range into boundary
and non-boundary nodes. Since there are only we boundary nodes we can
use the ArrayStorage for those yielding much faster query times.

include/engine/datafacade/algorithm_datafacade.hpp

@@ -65,6 +65,8 @@ template <> class AlgorithmDataFacade<MLD>
     // search graph access
     virtual unsigned GetNumberOfNodes() const = 0;
 
+    virtual unsigned GetMaxBorderNodeID() const = 0;
+
     virtual unsigned GetNumberOfEdges() const = 0;
 
     virtual unsigned GetOutDegree(const NodeID n) const = 0;

include/engine/datafacade/contiguous_internalmem_datafacade.hpp

@@ -675,6 +675,8 @@ template <> class ContiguousInternalMemoryAlgorithmDataFacade<MLD> : public Algo
     // search graph access
     unsigned GetNumberOfNodes() const override final { return query_graph.GetNumberOfNodes(); }
 
+    unsigned GetMaxBorderNodeID() const override final { return query_graph.GetMaxBorderNodeID(); }
+
     unsigned GetNumberOfEdges() const override final { return query_graph.GetNumberOfEdges(); }
 
     unsigned GetOutDegree(const NodeID n) const override final