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.BaseSpawner.v12.json

@@ -0,0 +1,123 @@
+{
+  "version": 12,
+  "type": "Server.Engines.Spawners.BaseSpawner",
+  "properties": [
+    {
+      "name": "Guid",
+      "type": "System.Guid",
+      "rule": "PrimitiveTypeMigrationRule"
+    },
+    {
+      "name": "ReturnOnDeactivate",
+      "type": "bool",
+      "usesSaveFlag": true,
+      "rule": "PrimitiveTypeMigrationRule",
+      "ruleArguments": [
+        ""
+      ]
+    },
+    {
+      "name": "Entries",
+      "type": "System.Collections.Generic.List\u003CServer.Engines.Spawners.SpawnerEntry\u003E",
+      "rule": "ListMigrationRule",
+      "ruleArguments": [
+        "Server.Engines.Spawners.SpawnerEntry",
+        "RawSerializableMigrationRule",
+        "DeserializationRequiresParent"
+      ]
+    },
+    {
+      "name": "WalkingRange",
+      "type": "int",
+      "rule": "PrimitiveTypeMigrationRule",
+      "ruleArguments": [
+        ""
+      ]
+    },
+    {
+      "name": "WayPoint",
+      "type": "Server.Items.WayPoint",
+      "usesSaveFlag": true,
+      "rule": "SerializableInterfaceMigrationRule"
+    },
+    {
+      "name": "Group",
+      "type": "bool",
+      "usesSaveFlag": true,
+      "rule": "PrimitiveTypeMigrationRule",
+      "ruleArguments": [
+        ""
+      ]
+    },
+    {
+      "name": "MinDelay",
+      "type": "System.TimeSpan",
+      "usesSaveFlag": true,
+      "rule": "PrimitiveTypeMigrationRule"
+    },
+    {
+      "name": "MaxDelay",
+      "type": "System.TimeSpan",
+      "usesSaveFlag": true,
+      "rule": "PrimitiveTypeMigrationRule"
+    },
+    {
+      "name": "Count",
+      "type": "int",
+      "rule": "PrimitiveTypeMigrationRule",
+      "ruleArguments": [
+        ""
+      ]
+    },
+    {
+      "name": "Team",
+      "type": "int",
+      "usesSaveFlag": true,
+      "rule": "PrimitiveTypeMigrationRule",
+      "ruleArguments": [
+        ""
+      ]
+    },
+    {
+      "name": "Running",
+      "type": "bool",
+      "rule": "PrimitiveTypeMigrationRule",
+      "ruleArguments": [
+        ""
+      ]
+    },
+    {
+      "name": "SpawnLocationIsHome",
+      "type": "bool",
+      "usesSaveFlag": true,
+      "rule": "PrimitiveTypeMigrationRule",
+      "ruleArguments": [
+        ""
+      ]
+    },
+    {
+      "name": "End",
+      "type": "System.DateTime",
+      "usesSaveFlag": true,
+      "rule": "PrimitiveTypeMigrationRule",
+      "ruleArguments": [
+        ""
+      ]
+    },
+    {
+      "name": "SpawnPositionMode",
+      "type": "Server.Engines.Spawners.SpawnPositionMode",
+      "usesSaveFlag": true,
+      "rule": "EnumMigrationRule"
+    },
+    {
+      "name": "MaxSpawnAttempts",
+      "type": "int",
+      "usesSaveFlag": true,
+      "rule": "PrimitiveTypeMigrationRule",
+      "ruleArguments": [
+        ""
+      ]
+    }
+  ]
+}