feat(timer): 添加定时器和冷却系统 (#325)

- 添加 ITimerService 接口和 TimerService 实现
- 支持一次性定时器和重复定时器
- 支持冷却系统 (startCooldown/isCooldownReady/getCooldownProgress)
- 添加 8 个蓝图节点:
  - StartCooldown, IsCooldownReady, GetCooldownProgress
  - ResetCooldown, GetCooldownInfo
  - HasTimer, CancelTimer, GetTimerRemaining

packages/timer/module.json

@@ -0,0 +1,23 @@
+{
+    "id": "timer",
+    "name": "@esengine/timer",
+    "globalKey": "timer",
+    "displayName": "Timer & Cooldown",
+    "description": "定时器和冷却系统 | Timer and cooldown system",
+    "version": "1.0.0",
+    "category": "Other",
+    "icon": "Timer",
+    "tags": ["timer", "cooldown", "delay", "schedule"],
+    "isCore": false,
+    "defaultEnabled": true,
+    "isEngineModule": true,
+    "canContainContent": false,
+    "platforms": ["web", "desktop"],
+    "dependencies": ["core"],
+    "exports": {
+        "components": [],
+        "systems": []
+    },
+    "outputPath": "dist/index.js",
+    "pluginExport": "TimerPlugin"
+}