📦️ build(deps): update python version constraint and pypi mirror

- enforce python version range to >=3.9 and <=3.12 in pyproject.toml
- switch pypi package source from tsinghua mirror to official pypi.org

pyproject.toml

@@ -7,7 +7,7 @@ name = "z-ai2api-python"
 version = "0.1.0"
 description = "一个为 Z.ai 提供 OpenAI API 兼容接口的 Python 代理服务"
 readme = "README.md"
-requires-python = ">=3.9"
+requires-python = ">=3.9,<=3.12"
 license = {text = "MIT"}
 authors = [
     {name = "Contributors"}