Tiles are now (mostly) pooled objects (#19112)

* Tiles are now (mostly) pooled objects

Floors no longer have a builtin_tile, but instead use PoolOrNew().

Also added a do-nothing SSpool so you can inspect the global pool.

* Entries for time keeping

* MORE STATISTICS

* Stat tracking, auto filling

* Code review I

* Code review II

* Code review III

code/controllers/subsystem/pool.dm

@@ -0,0 +1,48 @@
+var/datum/subsystem/pool/SSpool
+
+/datum/subsystem/pool
+	name = "Pool"
+	init_order = 20
+	flags = SS_BACKGROUND | SS_FIRE_IN_LOBBY
+	var/list/global_pool
+	var/list/pool_levels = list()
+	var/sum = 0
+
+	var/list/maintained_types = list(
+		/obj/item/stack/tile/plasteel = 100
+	)
+
+	var/list/stats_placed_in_pool = list()
+	var/list/stats_pooled_or_newed = list()
+	var/list/stats_reused = list()
+	var/list/stats_created_new = list()
+
+/datum/subsystem/pool/New()
+	NEW_SS_GLOBAL(SSpool)
+
+/datum/subsystem/pool/Initialize(timeofday)
+	global_pool = GlobalPool
+
+/datum/subsystem/pool/stat_entry(msg)
+	if(global_pool)
+		msg += "Types: [global_pool.len]|Total Pooled Objects: [sum]"
+	else
+		msg += "NULL POOL"
+	..(msg)
+
+/datum/subsystem/pool/fire()
+	sum = 0
+	for(var/type in global_pool + maintained_types)
+		var/list/L = global_pool[type]
+		var/required_number = maintained_types[type] || 0
+
+		// Update pool levels and tracker
+		var/amount = 0
+		if(L)
+			amount = L.len
+		sum += amount
+
+		// why yes, just inflate the pool at one item per tick
+		if(amount < required_number)
+			var/diver = new type
+			qdel(diver)