fix: Adds safety to corpses and cleans up quests (#1685)

### Summary
- Adds some more checks in case a corpse's owner is somehow null. Would like to eventually allow null owner corpses, but more work is needed.
- Cleans up variable unboxing and reassignment in quests. Also flattens quest logic. Still more work needs to be done.
- Codegens more quest items/mobiles.

Projects/UOContent/Migrations/Server.Engines.Quests.Hag.HagApprenticeCorpse.v0.json

@@ -0,0 +1,4 @@
+{
+  "version": 0,
+  "type": "Server.Engines.Quests.Hag.HagApprenticeCorpse"
+}