feat(draft_model): support draft_model for RemoteModelLoader (#6407)

Signed-off-by: wangyu <wangyu.steph@bytedance.com>

python/sglang/srt/managers/scheduler_update_weights_mixin.py

@@ -121,9 +121,16 @@ class SchedulerUpdateWeightsMixin:
         url = params["url"]
 
         worker = self.tp_worker.worker
-
         worker.model_runner.save_remote_model(url)
 
+        if self.draft_worker is not None:
+            draft_url = params.get("draft_url", None)
+            assert (
+                draft_url is not None
+            ), "draft_url must be provided when draft model is enabled"
+            draft_worker = self.draft_worker.worker
+            draft_worker.model_runner.save_remote_model(draft_url)
+
     def save_sharded_model(self, params):
         worker = self.tp_worker.worker