feat: Add spawn position caching and spiral scan optimization (#2295)

### Summary

Adds spawn position caching and optimization for constrained spawners (e.g., those near houses, water, or blocked terrain).

### Key features:
- Sector-based bitmap cache (32 bytes per 16x16 sector) stores valid spawn positions
- Spiral scan progressively discovers positions from spawner center outward
- Automatic mode detects constrained spawners after 5+ non-transient failures
- Prevents mob spawning inside private houses (allows public AoS buildings)
- Deduplicates sector lookups for multi-bounds spawners (RegionSpawner)
- Cache invalidation on house placement/demolition
- Moves SpawnBounds to Spawner

### New spawner properties:
- SpawnPositionMode: Automatic (default), Enabled, Disabled, Abandoned
- MaxSpawnAttempts: Configurable attempts before optimization engages (default: 5)

Projects/UOContent/Engines/Spawners/BaseSpawner.Migrations.cs

@@ -31,6 +31,38 @@ public abstract partial class BaseSpawner
         }
 
         _spawnLocationIsHome = false;
+
+        // New v12 fields default to automatic/default
+        _spawnPositionMode = SpawnPositionMode.Automatic;
+        _maxSpawnAttempts = DefaultMaxSpawnAttempts;
+    }
+
+    private void MigrateFrom(V11Content content)
+    {
+        _guid = content.Guid;
+        _returnOnDeactivate = content.ReturnOnDeactivate;
+        _entries = content.Entries;
+        _walkingRange = content.WalkingRange;
+        _wayPoint = content.WayPoint;
+        _group = content.Group;
+        _minDelay = content.MinDelay;
+        _maxDelay = content.MaxDelay;
+        _count = content.Count;
+        _team = content.Team;
+
+        // Moved to Spawner
+        if (this is Spawner spawner)
+        {
+            spawner.SpawnBounds = content.SpawnBounds;
+        }
+
+        _running = content.Running;
+        _spawnLocationIsHome = content.SpawnLocationIsHome;
+        _end = _running ? content.End : Core.Now;
+
+        // New v12 fields default to automatic/default
+        _spawnPositionMode = SpawnPositionMode.Automatic;
+        _maxSpawnAttempts = DefaultMaxSpawnAttempts;
     }
 
     private void Deserialize(IGenericReader reader, int version)