### What this PR does / why we need it?
Add ut for the cumsum_group_list function, which is related to the
precision issues stemming from the moe_mlp.py .
The ralated PR is https://github.com/vllm-project/vllm-ascend/pull/5025
### Does this PR introduce _any_ user-facing change?
No
- vLLM version: v0.12.0
- vLLM main:
ad32e3e19c
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Signed-off-by: tanqingshan (A) <50050625@china.huawei.com>
Co-authored-by: tanqingshan (A) <50050625@china.huawei.com>
Co-authored-by: wangxiyuan <wangxiyuan1007@gmail.com>
Co-authored-by: weijinqian0 <1184188277@qq.com>