Replaced the outside turfs with exoplanet ones for the digsite (#20066)

Replaced the outside turfs with exoplanet ones for the digsite.
Fixed some exoplanet areas not having an exoplanet base turf.
Wrote a unit test for exoplanet areas to ensure they have an exoplanet
base turf.

code/modules/overmap/exoplanets/biomes/barren.dm

@@ -4,7 +4,7 @@
 	spawn_types = list()
 
 /singleton/biome/barren/asteroid
-	turf_type = /turf/unsimulated/floor/asteroid/ash
+	turf_type = /turf/simulated/floor/exoplanet/asteroid/ash
 	generators = list(
 		WILDLIFE = list(POISSON_SAMPLE, 15)
 	)

code/modules/overmap/exoplanets/decor/_areas.dm

@@ -18,7 +18,7 @@
 
 /area/exoplanet/barren/asteroid
 	name = "\improper Asteroid Surface"
-	base_turf = /turf/unsimulated/floor/asteroid/ash
+	base_turf = /turf/simulated/floor/exoplanet/asteroid/ash
 
 /area/exoplanet/barren/raskara
 	name = "Raskara Surface"
@@ -71,7 +71,7 @@
 /area/exoplanet/lava
 	name = "\improper Planetary surface"
 	ambience = AMBIENCE_LAVA
-	base_turf = /turf/unsimulated/floor/asteroid/basalt
+	base_turf = /turf/simulated/floor/exoplanet/basalt
 
 /area/exoplanet/snow
 	ambience = list('sound/effects/wind/tundra0.ogg','sound/effects/wind/tundra1.ogg','sound/effects/wind/tundra2.ogg','sound/effects/wind/spooky0.ogg','sound/effects/wind/spooky1.ogg')

code/modules/overmap/exoplanets/decor/turfs/ceiling.dm

@@ -0,0 +1,6 @@
+/turf/simulated/floor/exoplanet/ceiling
+	name = "ceiling plating"
+	footstep_sound = /singleton/sound_category/plating_footstep
+	roof_type = null
+	icon = 'icons/turf/flooring/plating.dmi'
+	icon_state = "asteroidplating"

code/modules/overmap/exoplanets/themes/barren.dm

@@ -38,7 +38,7 @@
 	perlin_zoom = 21
 	surface_turfs = list(
 		/turf/simulated/mineral,
-		/turf/unsimulated/floor/asteroid/ash
+		/turf/simulated/floor/exoplanet/asteroid/ash
 	)
 
 	possible_biomes = list(