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/unit_tests/zas_tests.dm

@@ -74,7 +74,7 @@ GLOBAL_LIST_EMPTY(turfs_to_map_type)
 		var/t_msg = "Turf: [T] |  Location: [T.x] // [T.y] // [T.z]"
 
 		var/datum/gas_mixture/GM = T.return_air()
-		var/pressure = GM.return_pressure()
+		var/pressure = XGM_PRESSURE(GM)
 		var/temp = GM.temperature