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/Multis/Houses/BaseHouse.cs

@@ -3739,6 +3739,8 @@ namespace Server.Multis
                 Movable = false;
             }
 
+            public override bool SkipSerialization => true;
+
             public override string DefaultName => "a house transfer contract";
 
             public override void GetProperties(IPropertyList list)
@@ -3775,12 +3777,6 @@ namespace Server.Multis
                 }
             }
 
-            [AfterDeserialization(false)]
-            private void AfterDeserialization()
-            {
-                Delete();
-            }
-
             public override bool AllowSecureTrade(Mobile from, Mobile to, Mobile newOwner, bool accepted)
             {
                 if (!base.AllowSecureTrade(from, to, newOwner, accepted))

Projects/UOContent/Multis/Houses/PreviewHouse.cs

@@ -35,6 +35,8 @@ public partial class PreviewHouse : BaseMulti
         _timer.Start();
     }
 
+    public override bool SkipSerialization => true;
+
     public override void OnLocationChange(Point3D oldLocation)
     {
         base.OnLocationChange(oldLocation);
@@ -94,12 +96,6 @@ public partial class PreviewHouse : BaseMulti
         base.OnAfterDelete();
     }
 
-    [AfterDeserialization(false)]
-    private void AfterDeserialization()
-    {
-        Delete();
-    }
-
     private class DecayTimer : Timer
     {
         private readonly Item _item;