chore(lint): 修复 golangci-lint unused

- 移除 OpenAIGatewayHandler 未使用字段

- 删除并发缓存中未使用的 Redis 脚本常量

- 将仅供 unit 测试使用的 parseIntegralNumber 移入 unit build tag 文件

backend/internal/handler/openai_gateway_handler.go

@@ -28,7 +28,6 @@ type OpenAIGatewayHandler struct {
 	errorPassthroughService *service.ErrorPassthroughService
 	concurrencyHelper       *ConcurrencyHelper
 	maxAccountSwitches      int
-	cfg                     *config.Config
 }
 
 // NewOpenAIGatewayHandler creates a new OpenAIGatewayHandler
@@ -55,7 +54,6 @@ func NewOpenAIGatewayHandler(
 		errorPassthroughService: errorPassthroughService,
 		concurrencyHelper:       NewConcurrencyHelper(concurrencyService, SSEPingFormatComment, pingInterval),
 		maxAccountSwitches:      maxAccountSwitches,
-		cfg:                     cfg,
 	}
 }