refactor: token counter logic

relay/channel/cohere/relay-cohere.go

@@ -162,7 +162,7 @@ func cohereStreamHandler(c *gin.Context, resp *http.Response, info *relaycommon.
 		}
 	})
 	if usage.PromptTokens == 0 {
-		usage, _ = service.ResponseText2Usage(responseText, info.UpstreamModelName, info.PromptTokens)
+		usage = service.ResponseText2Usage(responseText, info.UpstreamModelName, info.PromptTokens)
 	}
 	return nil, usage
 }