[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>

pyproject.toml

@@ -21,3 +21,14 @@ requires = [
     "numba",
 ]
 build-backend = "setuptools.build_meta"
+
+[tool.pymarkdown]
+plugins.md004.style = "sublist" # ul-style
+plugins.md007.indent = 4 # ul-indent
+plugins.md007.start_indented = true # ul-indent
+plugins.md013.enabled = false # line-length
+plugins.md041.enabled = false # first-line-h1
+plugins.md033.enabled = false # inline-html
+plugins.md046.enabled = false # code-block-style
+plugins.md024.allow_different_nesting = true # no-duplicate-headers
+plugins.md029.enabled = false # ol-prefix