[core] clean up cudagraph batchsize padding logic (#10996)

Signed-off-by: youkaichao <youkaichao@gmail.com>

tests/models/decoder_only/language/test_mamba.py

@@ -5,7 +5,7 @@ Run `pytest tests/models/test_mamba.py`.
 import pytest
 from transformers import AutoModelForCausalLM, AutoTokenizer
 
-from vllm.config import VllmConfig
+from vllm.engine.arg_utils import EngineArgs
 from vllm.sampling_params import SamplingParams
 
 from ...utils import check_outputs_equal
@@ -200,7 +200,8 @@ def test_mamba_cache_cg_padding(
     # This test is for verifying that mamba cache is padded to CG captured
     # batch size. If it's not, a torch RuntimeError will be raised because
     # tensor dimensions aren't compatible
-    while len(example_prompts) == VllmConfig.get_graph_batch_size(
+    vllm_config = EngineArgs(model=model).create_engine_config()
+    while len(example_prompts) == vllm_config.pad_for_cudagraph(
             len(example_prompts)):
         example_prompts.append(example_prompts[0])