[Performance] Decode Offload improves the long texts performance 100% through dynamic block offload. (#17216)

Co-authored-by: zhangheng <hzh0425@apache.org>

python/sglang/srt/managers/cache_controller.py

@@ -576,6 +576,8 @@ class HiCacheController:
         model_name: Optional[str] = None,
         storage_backend_extra_config: Optional[dict] = None,
     ):
+        if storage_backend_extra_config is None:
+            storage_backend_extra_config = {}
 
         if is_dp_attention_enabled():
             self.tp_rank = get_attention_tp_rank()