refactor: Centralize stream handling and helper functions in relay package

relay/channel/cohere/relay-cohere.go

@@ -10,6 +10,7 @@ import (
 	"one-api/common"
 	"one-api/dto"
 	relaycommon "one-api/relay/common"
+	"one-api/relay/helper"
 	"one-api/service"
 	"strings"
 	"time"
@@ -103,7 +104,7 @@ func cohereStreamHandler(c *gin.Context, resp *http.Response, info *relaycommon.
 		}
 		stopChan <- true
 	}()
-	service.SetEventStreamHeaders(c)
+	helper.SetEventStreamHeaders(c)
 	isFirst := true
 	c.Stream(func(w io.Writer) bool {
 		select {