adds a unique species id unit test + cleans up some golem mischief (#66050)

code/modules/unit_tests/_unit_tests.dm

@@ -108,6 +108,7 @@
 #include "spawn_humans.dm"
 #include "spawn_mobs.dm"
 #include "species_config_sanity.dm"
+#include "species_unique_id.dm"
 #include "species_whitelists.dm"
 #include "stomach.dm"
 #include "strippable.dm"

code/modules/unit_tests/species_unique_id.dm

@@ -0,0 +1,14 @@
+/**
+ * Every species should use a species ID unique to it and it alone. This test runs through every subtype of /datum/species, and checks for a species ID.
+ * Every ID is written to a list, gathered_species_ids, and if a previously written ID is written again, this test will fail.
+ */
+/datum/unit_test/species_unique_id
+
+/datum/unit_test/species_unique_id/Run()
+	var/list/gathered_species_ids = list()
+	for(var/datum/species/species as anything in subtypesof(/datum/species))
+		var/species_id = initial(species.id)
+		if(gathered_species_ids[species_id])
+			Fail("Duplicate species ID! [species_id] is not unique to a single species.")
+		else
+			gathered_species_ids[species_id] = TRUE