Resets atmos between unit test runs (#85886)

## About The Pull Request

Talked with ghommie about the random spacemove BS and he made the point
that this is a basically impossible problem to solve by "fixing" each
point because so many things can change atmos or build up to change
atmos.

So instead of letting diffs stack up and potentially cause problems,
let's just clear the slate after every unit test

## Why It's Good For The Game

Should? solve our screenshot rando failures though it's hard to say for
sure cause idk maybe someone blew a hole in the testing area or
something.

code/modules/unit_tests/unit_test.dm

@@ -112,6 +112,16 @@ GLOBAL_VAR_INIT(focused_tests, focused_tests())
 	allocated += instance
 	return instance
 
+/// Resets the air of our testing room to its default
+/datum/unit_test/proc/restore_atmos()
+	var/area/working_area = run_loc_floor_bottom_left.loc
+	var/list/turf/to_restore = working_area.get_turfs_from_all_zlevels()
+	for(var/turf/open/restore in to_restore)
+		var/datum/gas_mixture/GM = SSair.parse_gas_string(restore.initial_gas_mix, /datum/gas_mixture/turf)
+		restore.copy_air(GM)
+		restore.temperature = initial(restore.temperature)
+		restore.air_update_turf(update = FALSE, remove = FALSE)
+
 /datum/unit_test/proc/test_screenshot(name, icon/icon)
 	if (!istype(icon))
 		TEST_FAIL("[icon] is not an icon.")
@@ -179,6 +189,7 @@ GLOBAL_VAR_INIT(focused_tests, focused_tests())
 	else
 
 		test.Run()
+		test.restore_atmos()
 
 		duration = REALTIMEOFDAY - duration
 		GLOB.current_test = null