This might have some interaction with issue1209 where we want to change the way the task is passed to the factory.

Currently, our landmark factories can compute landmarks for the initial state of a planning task. I would like to change their implementations to be able to compute landmarks for arbitrary states and make it the responsibility of their callers to specify they want landmarks for the initial state. While our code base currently has no use case to compute landmarks for other states, this enables future extensions, such as the inclusion of landmark cycle heuristics which recompute landmarks in every state encountered during search.