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/Migrations/Server.Engines.Spawners.Spawner.v1.json

@@ -0,0 +1,24 @@
+{
+  "version": 1,
+  "type": "Server.Engines.Spawners.Spawner",
+  "properties": [
+    {
+      "name": "UseSpiralScan",
+      "type": "bool",
+      "usesSaveFlag": true,
+      "rule": "PrimitiveTypeMigrationRule",
+      "ruleArguments": [
+        ""
+      ]
+    },
+    {
+      "name": "SpawnBounds",
+      "type": "Server.Rectangle3D",
+      "usesSaveFlag": true,
+      "rule": "PrimitiveUOTypeMigrationRule",
+      "ruleArguments": [
+        "Rect3D"
+      ]
+    }
+  ]
+}