[MIRROR] Reaction rates, pH, purity and more! Brings a heavily improved, less explosive and optimised fermichem to tg. (#3306)

* Reaction rates, pH, purity and more! Brings a heavily improved, less explosive and optimised fermichem to tg.

* a

Co-authored-by: Thalpy <33956696+Thalpy@users.noreply.github.com>
Co-authored-by: Gandalf2k15 <jzo123@hotmail.com>

code/controllers/subsystem/processing/reagents.dm

@@ -0,0 +1,42 @@
+//Used for active reactions in reagents/equilibrium datums
+
+PROCESSING_SUBSYSTEM_DEF(reagents)
+	name = "Reagents"
+	init_order = INIT_ORDER_REAGENTS
+	priority = FIRE_PRIORITY_REAGENTS
+	wait = 0.25 SECONDS //You might think that rate_up_lim has to be set to half, but since everything is normalised around delta_time, it automatically adjusts it to be per second. Magic!
+	flags = SS_KEEP_TIMING
+	runlevels = RUNLEVEL_GAME | RUNLEVEL_POSTGAME
+	///What time was it when we last ticked
+	var/previous_world_time = 0
+
+/datum/controller/subsystem/processing/reagents/Initialize()
+	. = ..()
+	//So our first step isn't insane
+	previous_world_time = world.time
+	//Build GLOB lists - see holder.dm
+	build_chemical_reagent_list()
+	build_chemical_reactions_list()
+	return 
+
+/datum/controller/subsystem/processing/reagents/fire(resumed = FALSE)
+	if (!resumed)
+		currentrun = processing.Copy()
+	//cache for sanic speed (lists are references anyways)
+	var/list/current_run = currentrun
+
+	//Attempt to realtime reactions in a way that doesn't make them overtly dangerous
+	var/delta_realtime = (world.time - previous_world_time)/10 //normalise to s from ds
+	previous_world_time = world.time
+
+	while(current_run.len)
+		var/datum/thing = current_run[current_run.len]
+		current_run.len--
+		if(QDELETED(thing))
+			stack_trace("Found qdeleted thing in [type], in the current_run list.")
+			processing -= thing
+		else if(thing.process(delta_realtime) == PROCESS_KILL) //we are realtime
+			// fully stop so that a future START_PROCESSING will work
+			STOP_PROCESSING(src, thing)
+		if (MC_TICK_CHECK)
+			return