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/mining/machine_processing.dm

@@ -24,7 +24,7 @@
 /obj/machinery/mineral/proc/register_input_turf()
 	input_turf = get_step(src, input_dir)
 	if(input_turf) // make sure there is actually a turf
-		RegisterSignal(input_turf, list(COMSIG_ATOM_INITIALIZED_ON, COMSIG_ATOM_ENTERED), PROC_REF(pickup_item))
+		RegisterSignals(input_turf, list(COMSIG_ATOM_INITIALIZED_ON, COMSIG_ATOM_ENTERED), PROC_REF(pickup_item))
 
 /// Unregisters signals that are registered the machine's input turf, if it has one.
 /obj/machinery/mineral/proc/unregister_input_turf()