Save 0.6-0.7s of init time by splitting registering lists of signals into its own proc, and optimizing QDELETED (#71056)

- Makes QDELETED use isnull(x) instead of !x, giving about 0.2 to 0.25s
of speed.
- Make disposal constructs only update icon state rather than go through
expensive overlay code. Unfortunately did not have much effect, but is
something they should've been doing nonetheless.
- Makes RegisterSignal only take signals directly as opposed to
allocating a fresh list of signals. Very few consumers actually used
this and it costs about 0.4s. Also I think this is just a bad API anyway
and that separate procs are important

`\bRegisterSignal\((.*)list\(` replaced with `RegisterSignals($1list(`

code/modules/modular_computers/file_system/programs/alarm.dm

@@ -19,7 +19,7 @@
 	//Or if we're on station. Otherwise, die.
 	var/list/allowed_areas = GLOB.the_station_areas + typesof(/area/mine)
 	alert_control = new(computer, list(ALARM_ATMOS, ALARM_FIRE, ALARM_POWER), listener_areas = allowed_areas)
-	RegisterSignal(alert_control.listener, list(COMSIG_ALARM_LISTENER_TRIGGERED, COMSIG_ALARM_LISTENER_CLEARED), PROC_REF(update_alarm_display))
+	RegisterSignals(alert_control.listener, list(COMSIG_ALARM_LISTENER_TRIGGERED, COMSIG_ALARM_LISTENER_CLEARED), PROC_REF(update_alarm_display))
 	return ..()
 
 /datum/computer_file/program/alarm_monitor/Destroy()