[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/developer_guide/modeling/adding_a_new_model.md

@@ -216,6 +216,7 @@ The first argument of `vllm.ModelRegistry.register_model()` indicates the unique
   ],
 }
 ```
+
 :::
 
 ## Step 3: Verification