[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/installation.md

@@ -190,6 +190,7 @@ git clone https://github.com/vllm-project/vllm-ascend.git
 cd vllm-ascend
 docker build -t vllm-ascend-dev-image:latest -f ./Dockerfile .
 ```
+
 :::
 
 ```{code-block} bash