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

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

tests/entrypoints/pooling/embed/test_cohere_online.py

@@ -7,10 +7,10 @@ embedding models, covering text embedding, embedding type conversions,
 response structure, batching, normalisation, and semantic similarity.
 """
 
-import base64
 import struct
 
 import numpy as np
+import pybase64 as base64
 import pytest
 import requests