[BUILD] Upgrade torch-npu to 2.5.1 (#661)

### What this PR does / why we need it?
The torch-npu 2.5.1 are published:
https://pypi.org/project/torch-npu/2.5.1/
It's time to remove all torch-npu dev version from vllm-ascend code base

### Does this PR introduce _any_ user-facing change?
Yes, using torch-npu 2.5.1

### How was this patch tested?
- [ ] CI passed
- [ ] Manually test
- [ ] Grep all `dev2025`

---------

Signed-off-by: Yikun Jiang <yikunkero@gmail.com>

README.zh.md

@@ -39,7 +39,7 @@ vLLM 昇腾插件 (`vllm-ascend`) 是一个由社区维护的让vLLM在Ascend NP
 - 软件：
   * Python >= 3.9
   * CANN >= 8.0.RC2
-  * PyTorch >= 2.5.1, torch-npu >= 2.5.1.dev20250320
+  * PyTorch >= 2.5.1, torch-npu >= 2.5.1
   * vLLM (与vllm-ascend版本一致)
 
 ## 开始使用