Astar port from TG

Created by: clusterfack

Direct port, totally compatible as nothing has touched literally any astar procs in years. They rewrote it after beepsky started lagging the fuck out of their server. And guess what, its the exact same problem that occurs for us on a regular basis.

Thanks TG, https://github.com/tgstation/-tg-station/pull/4138

Ideally this will mean I wont have to rewrite astar with navigation meshes based on ZAS zones. Which is something I would really like to not have to do, ya know? I will however do it if astar keeps lagging up in the long term, but this was rather easy to port over and should hopefully solve the issue well enough for it not to be a priority for a while.