Speeds up area power usage handling, and apc process(). Cleans up related code (#51002)

About The Pull Request

/area/proc/usage() attempts to give list-like access to a bunch of vars. Why not make it a list instead and avoid all the proc calls? Might be room for followup here, to do something to powered(), use_power() etc.

Some legacy machinery was ignoring the default machinery use_power pulling from the machine's power channel by default

Total power usage was unused, APCs ignored it in favor of calculating it themselves :)

I also renamed the defines because they were in the danger zone of being very common words.
Changelog

cl Naksu
code: optimized area power usage calculations.
/cl

code/modules/holodeck/computer.dm

@@ -67,6 +67,11 @@
 		return
 	else
 		linked.linked = src
+		var/area/my_area = get_area(src)
+		if(my_area)
+			linked.power_usage = my_area.power_usage
+		else
+			linked.power_usage = new /list(AREA_USAGE_LEN)
 
 	generate_program_list()
 	load_program(offline_program, FALSE, FALSE)
@@ -75,6 +80,7 @@
 	emergency_shutdown()
 	if(linked)
 		linked.linked = null
+		linked.power_usage = new /list(AREA_USAGE_LEN)
 	return ..()
 
 /obj/machinery/computer/holodeck/power_change()