CI: Set Up Testing Framework, Linter, and Formatter

[VoxleOne]

Task

Establish a robust foundation for code quality and testing by integrating standard development tools into the project.

Acceptance Criteria

• A testing framework (pytest) is added to the project.
• A tests/ directory is created with at least one initial unit test for a core function (e.g., in xreader.py or xcreator.py).
• A code formatter (black) is configured to ensure a consistent code style.
• A linter (ruff or flake8) is configured to automatically catch common errors and style issues.
• Scripts or configuration are added to pyproject.toml to make it easy to run these tools (e.g., pytest, black ., ruff .).

Rationale

Automated testing and linting are critical for maintaining a healthy codebase. They catch bugs early, ensure consistency, and make it easier for new contributors to write high-quality code.