Lag War Day 4: Under Pressure, High Voltage (#21878)

Replace /datum/gas_mixture/proc/return_pressure with XGM_PRESSURE(xgm)
macro. Having such a relatively simple statement contributing proc
overhead to procs called millions of times is ridiculous

Rename /datum/gas_mixture/proc/zburn to react, deleting the old react
which was just an alias for it. Free proc overhead

Turn check_combustibility into a macro CHECK_COMBUSTIBLE(is_cmb, xgm).
also rewrite it slightly so that it only needs to do one pass. Its a bit
nasty so I apologize for that, but speeeeed.

Delete most powernet and obj/machinery/power procs for handling power,
replacing them with macros. The fact that we were unironically calling a
draw_power() on APCs to call draw_power() on their terminals to call
draw_power() on their powernet every single process tick was insane.

Turn `between` into a macro alias for clamp() since the param order is
different

turn `Percent` into a macro AS_PCT

Rewrite significant chunks of update_canmove so its not quite as
horrifying of a proc and hopefully doesn't eat the entire mob subsystem
every movement now

code/modules/ventcrawl/ventcrawl.dm

@@ -174,7 +174,7 @@ GLOBAL_LIST_INIT(can_enter_vent_with, list(
 							if(BODYTEMP_HEAT_DAMAGE_LIMIT to INFINITY)
 								to_chat(src, SPAN_DANGER("You feel a searing heat coming from the vent!"))
 
-						switch(vent_found.air_contents.return_pressure())
+						switch(XGM_PRESSURE(vent_found.air_contents))
 							if(0 to HAZARD_LOW_PRESSURE)
 								to_chat(src, SPAN_DANGER("You feel a rushing draw pulling you into the vent!"))
 							if(HAZARD_LOW_PRESSURE to WARNING_LOW_PRESSURE)