chore: improve type checking (#62)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

- **New Features**
- Introduced type checking workflow for a Python package using GitHub
Actions.

- **Improvements**
- Enhanced type annotations across various modules for better code
clarity and maintainability.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Signed-off-by: Jinzhe Zeng <[email protected]>

.github/workflows/type-check.yml

@@ -0,0 +1,16 @@
+name: Type check
+on:
+  - push
+  - pull_request
+
+jobs:
+  type_check:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - name: Set up Python
+      uses: actions/setup-python@v5
+      with:
+        python-version: 3.12
+    - run: pip install uv
+    - run: uv run basedpyright --with .[typecheck]

dargs/__init__.py

@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 from .dargs import Argument, ArgumentEncoder, Variant
 
 __all__ = ["Argument", "Variant", "ArgumentEncoder"]