feat: Adds new decay system and SkipSerialization (#2311)

## Summary

- Replaces scan-based decay checking during world saves with an event-driven timer wheel scheduler
- Removes virtual property checks from serialization hot path, achieving 6-8x faster world saves

## Changes

### DecayScheduler (new):
- Timer wheel with 12 HashSet buckets (5-min intervals) + PriorityQueue for active processing
- O(1) register/unregister vs O(n) scan of all items
- Auto start/stop when items exist/empty
- Configurable tick interval with jitter to prevent system synchronization

### Item.cs:
- Added ScheduledDecayTime computed property
- Added UpdateDecayRegistration() called from SetLastMoved(), property setters, AddItem()/RemoveItem()
- Hooks in Visible, Movable, Spawner setters and Delete()

### World.cs:
- Removed _decayQueue, EnqueueForDecay(), ProcessDecay()
- ItemPersistence.Serialize() now tight loop without virtual calls

## Performance

| Metric        | Before     | After     | Improvement |
|---------------|------------|-----------|-------------|
| Items (230K)  | 245K ticks | 34K ticks | 8x faster   |
| Mobiles (43K) | 56K ticks  | 6K ticks  | 9x faster   |
| Total         | 302K ticks | 40K ticks | 7.5x faster |

## Configuration

decay.maxItemsPerTick = 250       # Items processed per tick
decay.tickInterval = 256ms        # Base processing interval
decay.bucketInterval = 5min       # Timer wheel bucket size
decay.jitterMaxMs = 25            # ±25ms tick jitter

Projects/UOContent/Spells/Seventh/GateTravel.cs

@@ -170,6 +170,8 @@ public partial class GateTravelMoongate : Moongate
         Timer.StartTimer(TimeSpan.FromSeconds(Core.T2A ? 30.0 : 10.0), Delete);
     }
 
+    public override bool SkipSerialization => true;
+
     [CommandProperty(AccessLevel.GameMaster)]
     public Moongate LinkedGate { get; set; }
 
@@ -200,10 +202,4 @@ public partial class GateTravelMoongate : Moongate
 
         base.UseGate(m);
     }
-
-    [AfterDeserialization(false)]
-    private void AfterDeserialization()
-    {
-        Delete();
-    }
 }

Projects/UOContent/Spells/Spellweaving/Mobiles/NatureFury.cs

@@ -36,6 +36,8 @@ public partial class NatureFury : BaseCreature
         ControlSlots = 1;
     }
 
+    public override bool SkipSerialization => true;
+
     public override bool DeleteCorpseOnDeath => Core.AOS;
     public override bool IsHouseSummonable => true;
 
@@ -65,10 +67,4 @@ public partial class NatureFury : BaseCreature
             Timer.StartTimer(TimeSpan.FromSeconds(7.0), DoEffects);
         }
     }
-
-    [AfterDeserialization(false)]
-    private void AfterDeserialization()
-    {
-        Delete();
-    }
 }