Add CI/test config, require Python 3.12, and update tests to package imports

[IliTheButterfly]

Motivation

• Enable automated test runs on push and pull requests and standardize the local/CI test environment.
• Move the project to a minimum of Python 3.12 and add dev test dependencies so tests run reproducibly.
• Align editor and test configuration with the src/ layout and package imports so tests import eb_macro_gen directly.

Description

• Added a GitHub Actions workflow at .github/workflows/tests.yml to run pytest on ubuntu-latest with Python 3.12.
• Updated pyproject.toml to require Python >=3.12, added a [project.optional-dependencies] dev group with pytest>=8, and added [tool.pytest.ini_options] with pythonpath and testpaths.
• Adjusted test modules in tests/ (for example test_objects.py, test_reverse_operators.py, and test_syntax_regressions.py) to import the package as eb_macro_gen instead of using src.-prefixed imports.
• Updated .vscode/settings.json to enable pytest, set python.testing.pytestArgs to run tests, and add src/ to python.analysis.extraPaths.
• Extended ReadMe.md to document the Python 3.12 requirement and provide instructions for running tests and configuring VS Code.

Testing

• Ran pytest (via pytest -q) against the test suite with the updated configuration.
• All tests completed successfully.

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Codex Task