Fix Bug 'get_cpu_copy not Implemented' in pd offloading mode (sgl-project#7982)

Author: hzh0425

python/sglang/srt/mem_cache/allocator.py

@@ -526,6 +526,12 @@ def clear(self):
         self.is_not_in_free_group = True
         self.free_group = []
 
+    def get_cpu_copy(self, indices):
+        return self._kvcache.get_cpu_copy(indices)
+
+    def load_cpu_copy(self, kv_cache_cpu, indices):
+        return self._kvcache.load_cpu_copy(kv_cache_cpu, indices)
+
 
 def alloc_extend_kernel_ascend(
     prefix_lens,