[Chore] Replace all base64 usages with faster pybase64 package (#37290)

Signed-off-by: Isotr0py <mozf@mail2.sysu.edu.cn>

tests/benchmarks/test_random_multimodal_dataset_video.py

@@ -1,12 +1,12 @@
 # SPDX-License-Identifier: Apache-2.0
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 
-import base64
 import os
 from tempfile import NamedTemporaryFile
 from typing import Any, cast
 
 import cv2
+import pybase64 as base64
 import pytest
 from transformers import AutoTokenizer, PreTrainedTokenizerBase