Refactors spell targeting to delegate it to a targeting datum (#16552)

Co-authored-by: AffectedArc07 <25063394+AffectedArc07@users.noreply.github.com>

code/modules/unit_tests/_unit_tests.dm

@@ -10,6 +10,7 @@
 #include "reagent_id_typos.dm"
 #include "rustg_version.dm"
 #include "spawn_humans.dm"
+#include "spell_targeting_test.dm"
 #include "sql.dm"
 #include "subsystem_init.dm"
 #include "subsystem_metric_sanity.dm"

code/modules/unit_tests/spell_targeting_test.dm

@@ -0,0 +1,10 @@
+/datum/unit_test/spell_targeting/Run()
+	var/list/bad_spells = list()
+	for(var/obj/effect/proc_holder/spell/S as anything in typesof(/obj/effect/proc_holder/spell))
+		if(initial(S.name) == "Spell")
+			continue // Skip abstract spells
+		S = new S
+		if(!S.targeting)
+			bad_spells += S
+	if(length(bad_spells))
+		Fail("Spells without targeting found: [bad_spells.Join(", ")]")