fix(spatial): 修复 GridAOI 可见性更新问题

- 修复 addObserver 时现有观察者无法检测到新实体的问题
- 修复实体远距离移动时观察者可见性未正确更新的问题
- 重构 demos 抽取公共测试工具

packages/tools/demos/src/utils.ts

@@ -0,0 +1,41 @@
+/**
+ * @zh Demo 测试工具函数
+ * @en Demo test utility functions
+ */
+
+/**
+ * @zh 断言条件为真，否则抛出错误
+ * @en Assert condition is true, otherwise throw error
+ */
+export function assert(condition: boolean, message: string): void {
+    if (!condition) throw new Error(`FAILED: ${message}`);
+    console.log(`  ✓ ${message}`);
+}
+
+/**
+ * @zh 打印测试章节标题
+ * @en Print test section header
+ */
+export function section(name: string): void {
+    console.log(`\n▶ ${name}`);
+}
+
+/**
+ * @zh 打印 Demo 开始标题
+ * @en Print demo start header
+ */
+export function demoHeader(name: string): void {
+    console.log('═══════════════════════════════════════');
+    console.log(`       ${name}`);
+    console.log('═══════════════════════════════════════');
+}
+
+/**
+ * @zh 打印 Demo 结束标题
+ * @en Print demo end header
+ */
+export function demoFooter(name: string): void {
+    console.log('\n═══════════════════════════════════════');
+    console.log(`  ${name}: ALL TESTS PASSED ✓`);
+    console.log('═══════════════════════════════════════\n');
+}