fix: Fixes various memory leaks and spells (#1786)

### Summary
- Fixes various memory leaks related to spells
- Fixes Spell Plague
- Added ability to determine if `sdi` should take effect for Spell Damage.
- Fixes animal form timer ticking non-stop while logged out.

Projects/UOContent/Network/Packets/IncomingAccountPackets.cs

@@ -341,7 +341,11 @@ public static class IncomingAccountPackets
         PlayerMurderSystem.OnLogin(m);
         AssistantHandler.OnLogin(m);
         VisibilityList.OnLogin(m);
-        PlayerMobile.OnLogin(m);
+
+        if (m is PlayerMobile pm)
+        {
+            PlayerMobile.OnLogin(pm);
+        }
         Account.OnLogin(m);
         GiftGiving.OnLogin(m);
         PreventInaccess.OnLogin(m);