Unit test to make sure all subsystems which initialize call parent (#36466)

code/modules/unit_tests/_unit_tests.dm

@@ -4,4 +4,5 @@
 #include "unit_test.dm"
 #include "reagent_recipe_collisions.dm"
 #include "reagent_id_typos.dm"
+#include "subsystem_init.dm"
 #endif

code/modules/unit_tests/subsystem_init.dm

@@ -0,0 +1,7 @@
+/datum/unit_test/subsystem_init/Run()
+	for(var/i in Master.subsystems)
+		var/datum/controller/subsystem/ss = i
+		if(ss.flags & SS_NO_INIT)
+			continue
+		if(!ss.initialized)
+			Fail("[ss]([ss.type]) is a subsystem meant to initialize but doesn't get set as initialized.")