fix no balance_serve import error

ktransformers/models/custom_cache.py

@@ -12,7 +12,10 @@ import torch.nn as nn
 import transformers
 from transformers import Cache, PretrainedConfig
 from typing import List, Optional, Dict, Any, Tuple
-from ktransformers.server.balance_serve.settings import sched_ext
+try:
+    from ktransformers.server.balance_serve.settings import sched_ext
+except:
+    print("no balance_serve")
 class StaticCache(transformers.StaticCache):
     """
     Static Cache class to be used with `torch.compile(model)`.
@@ -210,7 +213,7 @@ class KDeepSeekV3Cache(nn.Module):
         self.v_caches = []
         
 
-    def load(self, inference_context: sched_ext.InferenceContext): 
+    def load(self, inference_context: "sched_ext.InferenceContext"): 
         
         for i in range(self.config.num_hidden_layers):
             self.k_caches.append(