some more ai optimizations (#86975)

## About The Pull Request
ai controllers that have exhausted all their current behaviors now stop
processing until the next cycle, so we no longer need to do these checks
on every process fire. idle behaviors are now instead handled by a new
low priority subsystem. these are the costs before/after roughly 25
minutes into the round

![image](https://github.com/user-attachments/assets/28b93cf8-b929-432a-a17d-61cbd581cddf)


## Why It's Good For The Game
improves ai performance

## Changelog
🆑
/🆑

code/controllers/subsystem/unplanned_controllers.dm

@@ -0,0 +1,18 @@
+/// Handles making mobs perform lightweight "idle" behaviors such as wandering around when they have nothing planned
+SUBSYSTEM_DEF(unplanned_controllers)
+	name = "Unplanned AI Controllers"
+	flags = SS_POST_FIRE_TIMING|SS_BACKGROUND|SS_NO_INIT
+	priority = FIRE_PRIORITY_UNPLANNED_NPC
+	init_order = INIT_ORDER_AI_CONTROLLERS
+	wait = 0.25 SECONDS
+	runlevels = RUNLEVEL_GAME | RUNLEVEL_POSTGAME
+	///what ai status are we interested in
+	var/target_status = AI_STATUS_ON
+
+/datum/controller/subsystem/unplanned_controllers/stat_entry(msg)
+	msg = "Planning AIs:[length(GLOB.unplanned_controllers[target_status])]"
+	return ..()
+
+/datum/controller/subsystem/unplanned_controllers/fire(resumed)
+	for(var/datum/ai_controller/ai_controller as anything in GLOB.unplanned_controllers[target_status])
+		ai_controller.idle_behavior.perform_idle_behavior(wait * 0.1, ai_controller)