Currently, the PathData object can simultaneously hold DAGs and Walks, which is handy for certain temporal graphs but also complicates the code. It also comes at a performance penalty, as we (i) have to store the type of each path (walk or DAG) and (ii) treat each path differently when calculating the k-th order edge index. This prevents vector operations and is likely to eat up the performance gain that we get from the joint storage.

I propose to split those implementations into two classes WalkData and DAGData that both inherit from a common PathData base class.