the attempt then the planner fails. Otherwise the planner returns the path
+val dummy_point_planner : 'a PaplPlanner.point_t
+(** Straight line dummy planner.
+ The dummy planner immediately returns the path [\[a; b\]] as a solution to a
+ planning problem [(a, b)].
+ This planner is useful in simulations to quickly verify the layout of
+val dummy_sampler_planner : 'a PaplPlanner.sampler_t
+(** Straight line dummy planner for regions.
+ The planner samples the start and goal regions until an element [a] and [b]
+ has been retrieved from both, and then returns the path [\[a; b\]].
+ The planner fails if a region becomes empty before returning a value or if
+ none of the regions have returned a value before the stopping criteria says