add: add pyright as a static type checker

[arrowkato]

add pyright, its settings, and CI.
add sample unit tests with pytest

PR summaries

This pull request introduces several changes to enhance the Python development environment and improve code quality. The main changes include updates to configuration files, the addition of new dependencies, and the introduction of static type checking and testing utilities.

Configuration and Environment Setup:

• .devcontainer/devcontainer.json: Added new extensions for better TOML and Python support (tamasfe.even-better-toml, ms-python.vscode-pylance).
• .env.sample: Added a sample environment file for setting up the OpenAI API key.
• .python-version: Updated Python version from 3.12.3 to 3.12.6.

Static Type Checking:

• .github/workflows/pyright.yml: Added a GitHub Actions workflow for running Pyright for static type checking.
• .pre-commit-config.yaml: Configured pre-commit hook to run Pyright for static type checking.

Dependency Management:

• pyproject.toml: Added new dependencies (langchain-openai, langchain, python-dotenv) and configured Pyright settings for type checking.

Code Quality and Testing:

• pytest.ini: Added pytest markers for categorizing tests (e.g., slow, unit_test, integration).
• python_uv/calc.py: Added a new function add with type annotations and error handling.
• tests/test_calc.py: Added unit tests for the add function to check both correct and incorrect inputs.

These changes collectively improve the development setup, ensure better code quality through static type checking, and enhance testing capabilities.