[mem_cache] Move mamba state and retraction_backup into ReqKvInfo (#37164)

python/sglang/test/scripted_runtime/req_handle.py

@@ -42,7 +42,7 @@ class ScriptedReqHandle:
     @property
     def kv_pages(self) -> int:
         req = self.req
-        if req is None or not req.kv.is_held:
+        if req is None or not req.kv.holds_kv:
             return 0
         page_size = self.context.scheduler.page_size
         return (req.kv.kv_allocated_len + page_size - 1) // page_size