[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/contribution/index.md

@@ -13,6 +13,7 @@ But you can still set up dev env on Linux/Windows/macOS for linting and basic
 test as following commands:
 
 #### Run lint locally
+
 ```bash
 # Choose a base dir (~/vllm-project/) and set up venv
 cd ~/vllm-project/
@@ -103,7 +104,6 @@ If the PR spans more than one category, please include all relevant prefixes.
 You may find more information about contributing to vLLM Ascend backend plugin on [<u>docs.vllm.ai</u>](https://docs.vllm.ai/en/latest/contributing/overview.html).
 If you find any problem when contributing, you can feel free to submit a PR to improve the doc to help other developers.
 
-
 :::{toctree}
 :caption: Index
 :maxdepth: 1