[Feat] support persistent buffer for update_weight

Author: CyCle1024

tests/ray/test_update_weight.py

@@ -132,15 +132,7 @@ def test_lmdeploy_update_weight_and_generate(self):
         ray.get(train_controller.onload.remote(target="all"))
         ray.get(train_controller.offload.remote(["optimizer"]))
         ray.get(rollout_controller.onload_weights.remote())
-        import time
-        start_time = time.time()
         ray.get(train_controller.update_weights.remote())
-        end_time = time.time()
-        print(f"Update weights time 1: {end_time - start_time} seconds")
-        start_time = time.time()
-        ray.get(train_controller.update_weights.remote())
-        end_time = time.time()
-        print(f"Update weights time 2: {end_time - start_time} seconds")
         ray.get(train_controller.offload.remote(["model"]))
         ray.get(rollout_controller.onload_kvcache.remote())