Warns for genturf failures more clearly, makes planetary cleanup better (#83809)

## About The Pull Request

Ok so like, we recently had an issue where a genturf was not being
replaced, which fucked ALL of icemoon's atmosphere.

The fix was to not use a genturf with a conditionally generating area,
but that aside. (why is it CONDITIONAL TIME GREEEEEN)

Planetary turfs should act like immutable ones when roundstart
equalizing.

In addition, we should test to ensure none leaves genturfs floating
around post roundstart to avoid this sorta issue.

---------

Co-authored-by: Afevis <ShizCalev@users.noreply.github.com>

code/modules/atmospherics/environmental/LINDA_turf_tile.dm

@@ -470,11 +470,19 @@
 	for(var/turf/open/group_member as anything in turf_list)
 		//Cache?
 		var/datum/gas_mixture/turf/mix = group_member.air
-		if (roundstart && istype(group_member.air, /datum/gas_mixture/immutable))
-			imumutable_in_group = TRUE
-			shared_mix.copy_from(group_member.air) //This had better be immutable young man
-			shared_gases = shared_mix.gases //update the cache
-			break
+		if (roundstart)
+			if(istype(group_member.air, /datum/gas_mixture/immutable))
+				imumutable_in_group = TRUE
+				shared_mix.copy_from(group_member.air) //This had better be immutable young man
+				shared_gases = shared_mix.gases //update the cache
+				break
+			// If we're planetary use THAT mix, and stop here
+			if(group_member.planetary_atmos)
+				imumutable_in_group = TRUE
+				var/datum/gas_mixture/planetary_mix = SSair.planetary[group_member.initial_gas_mix]
+				shared_mix.copy_from(planetary_mix)
+				shared_gases = shared_mix.gases // Cache update
+				break
 		//"borrowing" this code from merge(), I need to play with the temp portion. Lets expand it out
 		//temperature = (giver.temperature * giver_heat_capacity + temperature * self_heat_capacity) / combined_heat_capacity
 		var/capacity = mix.heat_capacity()

code/modules/unit_tests/_unit_tests.dm

@@ -204,6 +204,7 @@
 #include "organ_bodypart_shuffle.dm"
 #include "organ_set_bonus.dm"
 #include "organs.dm"
+#include "orphaned_genturf.dm"
 #include "outfit_sanity.dm"
 #include "oxyloss_suffocation.dm"
 #include "paintings.dm"

code/modules/unit_tests/orphaned_genturf.dm

@@ -0,0 +1,7 @@
+/// Ensures we do not leave genturfs sitting around post work
+/// They serve as notice to the mapper and have no functionality, but it's good to make note of it here
+/datum/unit_test/orphaned_genturf
+
+/datum/unit_test/orphaned_genturf/Run()
+	for(var/turf/open/genturf/orphaned in ALL_TURFS())
+		TEST_FAIL("Floating genturf ([orphaned.type]) detected at ([orphaned.x], [orphaned.y], [orphaned.z]) : [orphaned.loc.type]. Why was it not replaced?")