[TASK]: Improve edge routing performance

[mwdchang]

Edge routing currently starts from scratch every time we route an edge, this can be very expensive if there are moderate to high number of nodes/edges, say > 100.

I think we can improve this: Because the "obstacles" generally do not change, their grid map in the algorithm should be able to be computed and cached ahead of time, kind of like a memoization kind of thing.