ci: Add GitHub Actions CI workflow

[SIVALANAGASHANKARNIVAS]

Summary

This PR addresses #23 by implementing a comprehensive GitHub Actions CI workflow for the CLU project.

Changes

Added .github/workflows/ci.yml with:

Test Job

• Runs on Ubuntu and macOS
• Tests against Python 3.8, 3.9, 3.10, 3.11, and 3.12
• Installs project dependencies with pip install -e .[dev]
• Runs pytest with coverage reporting
• Uploads coverage reports to Codecov

Lint Job

• Runs on Ubuntu with Python 3.11
• Installs flake8 and pylint
• Runs flake8 for code style checking

Triggers

• Push events to master and main branches
• Pull request events targeting master and main branches

Closes #23