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

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

tests/renderers/test_sparse_tensor_validation.py

@@ -5,9 +5,9 @@ Tests verify that malicious sparse tensors are rejected before they can trigger
 out-of-bounds memory writes during to_dense() operations.
 """
 
-import base64
 import io
 
+import pybase64 as base64
 import pytest
 import torch