[1/2/N] Enable pymarkdown and python __init__ for lint system (#2011)

### What this PR does / why we need it?
1. Enable pymarkdown check
2. Enable python `__init__.py` check for vllm and vllm-ascend
3. Make clean code

### How was this patch tested?


- vLLM version: v0.9.2
- vLLM main:
29c6fbe58c

---------

Signed-off-by: wangli <wangli858794774@gmail.com>

docs/source/tutorials/single_node_300i.md

@@ -80,6 +80,7 @@ curl http://localhost:8000/v1/completions \
     "temperature": 0.6
   }'
 ```
+
 ::::
 
 ::::{tab-item} Qwen/Qwen2.5-7B-Instruct
@@ -318,6 +319,7 @@ if __name__ == "__main__":
 :::::
 
 Run script:
+
 ```bash
 python example.py
 ```