Further process tweaks

- Integrates Volundr's btime library and associated process scheduler
changes.
- btime is implemented separately from the process scheduler, as precise
time measurement is also useful elsewhere.
- `TimeOfHour` is no longer internally throttled; throttling is instead
done by `SCHECK`.
- If btime's `gettime` cannot be called at world startup, an error will
be output and the world will stop.
- Retains the change to schedule processes according to game time,
rather than real time.
- Removes the (now unused) update queue files.
- Removes the process scheduler testing files.
- These are standalone tests for the process scheduler, completely
unrelated to its use in the full codebase. We never used them.
- Moves the process scheduler defines into __DEFINES.
- Makes the lighting process run once before the round starts.
- Renames `scheck` to `sleepCheck`, to ensure any code that tries to use
`scheck` will fail to compile.
- Adds `SCHECK` and `SCHECK_EVERY` macros that skip calling `sleepCheck`
entirely until a specified number of `SCHECK`s (50 by default) have been
called.
- Makes most processes iterate using their `last_object` variable,
allowing hang recovery to show the type that caused the hang.
- Makes processes output an error when they filter out a type they
refuse to process.
- Rolls the recently-added alarm subsystem into the alarm process.
- Removes the now unused subsystems code.

code/controllers/Processes/air.dm

@@ -54,27 +54,27 @@ var/global/datum/controller/process/air_system/air_master
 	last_hotspots = hotspots.len
 	for(var/obj/effect/hotspot/H in hotspots)
 		H.process()
-		scheck()
+		SCHECK
 
 /datum/controller/process/air_system/proc/process_super_conductivity()
 	last_asc = active_super_conductivity.len
 	for(var/turf/simulated/T in active_super_conductivity)
 		T.super_conduct()
-		scheck()
+		SCHECK
 
 /datum/controller/process/air_system/proc/process_high_pressure_delta()
 	last_hpd = high_pressure_delta.len
 	for(var/turf/T in high_pressure_delta)
 		T.high_pressure_movements()
 		T.pressure_difference = 0
-		scheck()
+		SCHECK
 	high_pressure_delta.Cut()
 
 /datum/controller/process/air_system/proc/process_active_turfs()
 	last_active = active_turfs.len
 	for(var/turf/simulated/T in active_turfs)
 		T.process_cell()
-		scheck()
+		SCHECK
 
 /datum/controller/process/air_system/proc/remove_from_active(var/turf/simulated/T)
 	if(istype(T))
@@ -123,11 +123,11 @@ var/global/datum/controller/process/air_system/air_master
 		EG.breakdown_cooldown ++
 		if(EG.breakdown_cooldown == 10)
 			EG.self_breakdown()
-			scheck()
+			SCHECK
 			return
 		if(EG.breakdown_cooldown > 20)
 			EG.dismantle()
-		scheck()
+		SCHECK
 
 /datum/controller/process/air_system/proc/setup_overlays()
 	plmaster = new /obj/effect/overlay()