feat(usage): add test script API with refactored execution logic

- Add private helper method `execute_and_format_usage_result` to eliminate code duplication
- Refactor `query_usage` to use helper method instead of duplicating result processing
- Add new `test_usage_script` method to test temporary script without saving
- Add backend command `test_usage_script` accepting script content as parameter
- Register new command in lib.rs invoke_handler
- Add frontend `usageApi.testScript` method to call the new backend API
- Update `UsageScriptModal.handleTest` to test current editor content instead of saved script
- Improve DX: users can now test script changes before saving

src/components/UsageScriptModal.tsx

@@ -144,7 +144,15 @@ const UsageScriptModal: React.FC<UsageScriptModalProps> = ({
   const handleTest = async () => {
     setTesting(true);
     try {
-      const result = await usageApi.query(provider.id, appId);
+      // 使用当前编辑器中的脚本内容进行测试
+      const result = await usageApi.testScript(
+        provider.id,
+        appId,
+        script.code,
+        script.timeout,
+        script.accessToken,
+        script.userId
+      );
       if (result.success && result.data && result.data.length > 0) {
         // 显示所有套餐数据
         const summary = result.data