Fix SSE timeout will affected by http.Server 's WriteTimeout (#5024)

Co-authored-by: csbzy <chenshaobo65@mail.com>
Co-authored-by: Kevin Wan <wanjunfeng@gmail.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

rest/internal/response/withcoderesponsewriter.go

@@ -59,3 +59,8 @@ func (w *WithCodeResponseWriter) WriteHeader(code int) {
 	w.Writer.WriteHeader(code)
 	w.Code = code
 }
+
+// Unwrap returns the underlying ResponseWriter.
+func (w *WithCodeResponseWriter) Unwrap() http.ResponseWriter {
+	return w.Writer
+}