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/components/StreamingAnchorComponent.ts

@@ -0,0 +1,61 @@
+import { Component, ECSComponent, Serializable, Serialize, Property } from '@esengine/ecs-framework';
+
+/**
+ * 流式锚点组件
+ *
+ * Marks an entity as a streaming anchor point.
+ * Chunks are loaded/unloaded based on distance to anchors.
+ *
+ * 标记实体作为流式加载锚点。通常挂载在玩家或摄像机实体上，
+ * 系统会根据锚点位置加载/卸载周围区块。
+ */
+@ECSComponent('StreamingAnchor')
+@Serializable({ version: 1, typeId: 'StreamingAnchor' })
+export class StreamingAnchorComponent extends Component {
+    /**
+     * 锚点权重
+     *
+     * Weight multiplier for this anchor's load radius.
+     * Higher values mean larger load radius around this anchor.
+     */
+    @Serialize()
+    @Property({ type: 'number', label: 'Weight', min: 0.1, max: 10 })
+    weight: number = 1.0;
+
+    /**
+     * 是否启用预加载
+     *
+     * Enable directional prefetching based on movement.
+     */
+    @Serialize()
+    @Property({ type: 'boolean', label: 'Enable Prefetch' })
+    bEnablePrefetch: boolean = true;
+
+    /**
+     * 上一帧位置 X
+     *
+     * Previous frame X position for velocity calculation.
+     */
+    previousX: number = 0;
+
+    /**
+     * 上一帧位置 Y
+     *
+     * Previous frame Y position for velocity calculation.
+     */
+    previousY: number = 0;
+
+    /**
+     * 速度 X 分量
+     *
+     * X component of velocity (units per second).
+     */
+    velocityX: number = 0;
+
+    /**
+     * 速度 Y 分量
+     *
+     * Y component of velocity (units per second).
+     */
+    velocityY: number = 0;
+}