Changes astar from using a turf var to a proc list (#21947)

Fixes a runtime related to two bots trying to path through the same turf, and should improve the overall cost.

The runtime was caused by one bot pathing through a square, then getting check tick sleeped and the second both pathing through the same square.

Because the pnode lived on the turf it would assume that it had already seen that turf and try to resort the open heap, causing a bad index runtime as that turf was not in it's own open list

code/orphaned_procs/AStar.dm

@@ -43,7 +43,6 @@ Actual Adjacent procs :
 	g = pg
 	h = ph
 	f = g + h
-	source.PNode = src
 	nt = pnt
 
 /PathNode/proc/calc_f()
@@ -70,7 +69,7 @@ Actual Adjacent procs :
 
 //the actual algorithm
 /proc/AStar(caller, end, dist, maxnodes, maxnodedepth = 30, mintargetdist, adjacent = /turf/proc/reachableAdjacentTurfs, id=null, turf/exclude=null, simulated_only = 1)
-
+	var/list/pnodelist = list()
 	//sanitation
 	var/start = get_turf(caller)
 	if(!start)
@@ -123,23 +122,25 @@ Actual Adjacent procs :
 				continue
 
 			var/newg = cur.g + call(cur.source,dist)(T)
-			if(!T.PNode) //is not already in open list, so add it
-				open.Insert(new /PathNode(T,cur,newg,call(T,dist)(end),cur.nt+1))
+
+			var/PathNode/P = pnodelist[T]
+			if(!P)
+			 //is not already in open list, so add it
+				var/PathNode/newnode = new /PathNode(T,cur,newg,call(T,dist)(end),cur.nt+1)
+				open.Insert(newnode)
+				pnodelist[T] = newnode
 			else //is already in open list, check if it's a better way from the current turf
-				if(newg < T.PNode.g)
-					T.PNode.prevNode = cur
-					T.PNode.g = newg
-					T.PNode.calc_f()
-					T.PNode.nt = cur.nt + 1
-					open.ReSort(T.PNode)//reorder the changed element in the list
+				if(newg < P.g)
+					P.prevNode = cur
+					P.g = newg
+					P.calc_f()
+					P.nt = cur.nt + 1
+					open.ReSort(P)//reorder the changed element in the list
 		CHECK_TICK
 
 
 	//cleaning after us
-	for(var/PathNode/PN in open.L)
-		PN.source.PNode = null
-	for(var/turf/T in closed)
-		T.PNode = null
+	pnodelist = null
 
 	//reverse the path to get it from start to finish
 	if(path)