refactor: 重构模型测试错误解析逻辑并修复用量统计变量引用

- 将 ModelsTab 和 ModelAliasesTab 中重复的错误解析逻辑提取到 errorParser.ts
- 添加 parseTestModelError 函数统一处理测试响应错误
- 为 testModel API 添加 TypeScript 类型定义 (TestModelRequest/TestModelResponse)
- 修复 endpoint_checker.py 中 usage_data 变量引用错误

src/api/handlers/base/endpoint_checker.py

@@ -1243,7 +1243,7 @@ class EndpointCheckOrchestrator:
                     api_format=api_format,
                 )
 
-                logger.info(f"[{request.api_format}] Usage calculated successfully: {usage_data}")
+                logger.info(f"[{request.api_format}] Usage calculated successfully: {result.usage_data}")
             except Exception as e:
                 logger.error(f"[{request.api_format}] Failed to calculate usage: {e}")
                 import traceback