[Multimodal][Perf] Use pybase64 instead of base64 (#7724)

python/sglang/srt/entrypoints/http_server_engine.py

@@ -1,4 +1,3 @@
-import base64
 import copy
 import dataclasses
 import multiprocessing
@@ -7,6 +6,7 @@ import threading
 import time
 from typing import Any, Dict, List, Optional, Tuple, Union
 
+import pybase64
 import requests
 import torch
 import torch.distributed as dist