fix: 修复请求体过大处理和冗余代码问题

1. 修复OpenAI TTS接口的请求体过大错误提示，返回正确的状态码和提示信息
2. 删除volcano适配器中无用的空循环扫描代码
3. 修正constants.go的包声明重复空格问题

adapter/volcano/volcano.go

@@ -132,8 +132,6 @@ func Synthesis(config *dto.ByteDanceTTSConfig, httpClient *HTTPClient, text stri
 			if v3Resp.Usage != nil {
 				log.Printf("TTS synthesis completed, usage: %+v", v3Resp.Usage)
 			}
-			for scanner.Scan() {
-			}
 			break
 		}
 

common/constants.go

@@ -1,4 +1,4 @@
-package common
+package common
 
 import "time"
 

controller/tts.go

@@ -58,10 +58,11 @@ func OpenaiTTSHandler(w http.ResponseWriter, r *http.Request) {
 	r.Body = http.MaxBytesReader(w, r.Body, common.MaxRequestBodySize)
 	body, err := io.ReadAll(r.Body)
 	if err != nil {
-		if strings.Contains(err.Error(), "request body too large") {
-			return
-		}
-		http.Error(w, "Failed to read request body", http.StatusBadRequest)
+	if strings.Contains(err.Error(), "request body too large") {
+		http.Error(w, fmt.Sprintf("Request body too large (max %d bytes)", common.MaxRequestBodySize), http.StatusRequestEntityTooLarge)
+		return
+	}
+	http.Error(w, "Failed to read request body", http.StatusBadRequest)
 		return
 	}