stdcm: use the A* heuristic to discard paths that can't be fast enough

[eckter]

Requires #2818, this can't be done if the coordinates don't match the distances.

We discard paths that are longer than x seconds (a given parameter), but we only check the known run time. We should also estimate the fastest remaining run time to go from the current point to the destination, and discard the path if it can't lead to a solution in time.