fix: move image count n to OtherRatio to prevent double-counting

The previous commit commented out AddOtherRatio("n") in the Ali
adaptor to fix double-counting but this could cause billing evasion
when n is specified via extra["parameters"] instead of request.N.

Root cause: ImagePriceRatio in GetTokenCountMeta() already included
n, AND channel adaptors added OtherRatio("n"), resulting in n²
billing.

Proper fix:
- Remove n from ImagePriceRatio (keep sizeRatio * qualityRatio only)
- In ImageHelper, add default OtherRatio("n") when adaptor hasn't
  set one; set fallback tokens to 1 (base unit)
- Restore Ali adaptor's AddOtherRatio("n") — it uses actual upstream
  parameters/response count, preventing billing evasion

relay/channel/ali/image.go

@@ -54,10 +54,9 @@ func oaiImage2AliImageRequest(info *relaycommon.RelayInfo, request dto.ImageRequ
 		}
 	}
 
-	// 检查n参数
-	// if imageRequest.Parameters.N != 0 {
-	// 	info.PriceData.AddOtherRatio("n", float64(imageRequest.Parameters.N))
-	// }
+	if imageRequest.Parameters.N != 0 {
+		info.PriceData.AddOtherRatio("n", float64(imageRequest.Parameters.N))
+	}
 
 	// 同步图片模型和异步图片模型请求格式不一样
 	if isSync {
@@ -328,13 +327,11 @@ func aliImageHandler(a *Adaptor, c *gin.Context, resp *http.Response, info *rela
 	}
 
 	imageResponses := responseAli2OpenAIImage(c, aliResponse, originRespBody, info, responseFormat)
-	// 可能生成多张图片，修正计费数量n
-	// 注释掉，否则会导致多次扣费用
-	// if aliResponse.Usage.ImageCount != 0 {
-	// 	info.PriceData.AddOtherRatio("n", float64(aliResponse.Usage.ImageCount))
-	// } else if len(imageResponses.Data) != 0 {
-	// 	info.PriceData.AddOtherRatio("n", float64(len(imageResponses.Data)))
-	// }
+	if aliResponse.Usage.ImageCount != 0 {
+		info.PriceData.AddOtherRatio("n", float64(aliResponse.Usage.ImageCount))
+	} else if len(imageResponses.Data) != 0 {
+		info.PriceData.AddOtherRatio("n", float64(len(imageResponses.Data)))
+	}
 	jsonResponse, err := common.Marshal(imageResponses)
 	if err != nil {
 		return types.NewError(err, types.ErrorCodeBadResponseBody), nil