[Core] Performance: Use list[np.ndarray] instead of list[list[int]] for output tokens for GC optimization (#26368)

Signed-off-by: Jialin Ouyang <Jialin.Ouyang@gmail.com>

tests/v1/core/test_async_scheduler.py

@@ -2,6 +2,7 @@
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 from collections import deque
 
+import numpy as np
 import pytest
 
 from vllm.v1.core.sched.output import SchedulerOutput
@@ -21,7 +22,7 @@ def _make_model_runner_output(
     return ModelRunnerOutput(
         req_ids=req_ids,
         req_id_to_index={req_id: i for i, req_id in enumerate(req_ids)},
-        sampled_token_ids=[[i] for i in range(len(req_ids))],
+        sampled_token_ids=[np.array([i]) for i in range(len(req_ids))],
         logprobs=None,
         prompt_logprobs_dict={},
         pooler_output=[],