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/Spells/Fourth/ArchProtection.cs

@@ -117,24 +117,16 @@ namespace Server.Spells.Fourth
 
         private class InternalTimer : Timer
         {
-            private readonly Mobile m_Owner;
+            private readonly Mobile _owner;
 
-            public InternalTimer(Mobile target, Mobile caster) : base(TimeSpan.FromSeconds(0))
-            {
-                var time = caster.Skills.Magery.Value * 1.2;
-                if (time > 144)
-                {
-                    time = 144;
-                }
+            public InternalTimer(Mobile target, Mobile caster) : base(GetDelay(caster)) => _owner = target;
 
-                Delay = TimeSpan.FromSeconds(time);
-
-                m_Owner = target;
-            }
+            private static TimeSpan GetDelay(Mobile caster) =>
+                TimeSpan.FromSeconds(Math.Min(144, caster.Skills.Magery.Value * 1.2));
 
             protected override void OnTick()
             {
-                RemoveEntry(m_Owner);
+                RemoveEntry(_owner);
             }
         }
     }