Add GitHub Actions workflow for testing

[abdellatifLabr]

Summary

• Adds GitHub Actions workflow to run tests on push and pull requests
• Tests against Python 3.10, 3.11, and 3.12 on ubuntu-latest
• Runs linter (flake8) and pytest on each CI run

Details

• Trigger: push to main branch and pull requests
• Matrix strategy: Python 3.10, 3.11, 3.12
• Jobs: lint check with make lint and tests with pytest