chore: 代码质量修复 + CI升级

- black 格式化 (1 file)
- isort 排序修复 (30 files, --profile black)
- 升级 actions/checkout v4 → v6 (全部 3 个 workflow)
- 添加 pyproject.toml (black/isort 配置)
- isort CI 命令添加 --profile black 参数
- 114 测试全部通过

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

.github/workflows/python-tests.yml

@@ -26,7 +26,7 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Set up Python
         uses: actions/setup-python@v5