machinery_process() & auto_use_power efficiency tweaks (#2657)

changes:

Machinery now uses machinery_process() instead of process(), allowing machines to be put into SSprocessing-style lists in addition to the machinery list.
Automatic power calculations now involve less proc-calls.

code/modules/mob/living/silicon/ai/ai.dm

@@ -304,7 +304,7 @@ var/list/ai_verbs_default = list(
 	. = ..()
 	powered_ai = null
 
-/obj/machinery/ai_powersupply/process()
+/obj/machinery/ai_powersupply/machinery_process()
 	if(!powered_ai || powered_ai.stat == DEAD)
 		qdel(src)
 		return

code/modules/mob/living/silicon/robot/drone/drone_manufacturer.dm

@@ -34,7 +34,7 @@
 	if (stat & NOPOWER)
 		icon_state = "drone_fab_nopower"
 
-/obj/machinery/drone_fabricator/process()
+/obj/machinery/drone_fabricator/machinery_process()
 
 	if(!ROUND_IS_STARTED)
 		return