Fix hash collision for multi modal models (#2256)

python/sglang/srt/managers/session_controller.py

@@ -10,10 +10,7 @@
 # limitations under the License.
 # ==============================================================================
 
-import copy
 import uuid
-from dataclasses import dataclass
-from typing import Optional
 
 from sglang.srt.managers.io_struct import TokenizedGenerateReqInput
 from sglang.srt.managers.schedule_batch import FINISH_ABORT, List, Req