feat(world-streaming): 添加世界流式加载系统 (#288)

实现基于区块的世界流式加载系统，支持开放世界游戏：

运行时包 (@esengine/world-streaming):
- ChunkComponent: 区块实体组件，包含坐标、边界、状态
- StreamingAnchorComponent: 流式锚点组件（玩家/摄像机）
- ChunkLoaderComponent: 流式加载配置组件
- ChunkStreamingSystem: 区块加载/卸载调度系统
- ChunkCullingSystem: 区块可见性剔除系统
- ChunkManager: 区块生命周期管理服务
- SpatialHashGrid: 空间哈希网格
- ChunkSerializer: 区块序列化

编辑器包 (@esengine/world-streaming-editor):
- ChunkVisualizer: 区块可视化覆盖层
- ChunkLoaderInspectorProvider: 区块加载器检视器
- StreamingAnchorInspectorProvider: 流式锚点检视器
- WorldStreamingPlugin: 完整插件导出

packages/world-streaming/src/index.ts

@@ -0,0 +1,53 @@
+/**
+ * @esengine/world-streaming
+ *
+ * World streaming and chunk management system for open world games.
+ *
+ * 世界流式加载和区块管理系统，用于开放世界游戏。
+ */
+
+// Types
+export {
+    EChunkState,
+    EChunkPriority,
+    DEFAULT_STREAMING_CONFIG
+} from './types';
+
+export type {
+    IChunkCoord,
+    IChunkBounds,
+    IChunkData,
+    ISerializedEntity,
+    IChunkInfo,
+    IChunkLoadRequest,
+    IStreamingConfig
+} from './types';
+
+// Components
+export {
+    ChunkComponent,
+    StreamingAnchorComponent,
+    ChunkLoaderComponent
+} from './components';
+
+// Systems
+export {
+    ChunkStreamingSystem,
+    ChunkCullingSystem
+} from './systems';
+
+// Services
+export {
+    SpatialHashGrid,
+    ChunkSerializer,
+    ChunkManager
+} from './services';
+
+export type {
+    IChunkSerializer,
+    IChunkDataProvider,
+    IChunkManagerEvents
+} from './services';
+
+// Module
+export { WorldStreamingModule, worldStreamingModule } from './WorldStreamingModule';