Add continuous integration via github actions

[jphaupt]

Introduces a @pytest.mark.slow for slow tests, which were tested on my (Lenovo ThinkPad X1 Yoga 6) with pytest pytest -q --durations=0. To run the test suite without these, do pytest -m 'not slow' --durations=0

This PR introduces a CI/CD workflow where for every non-draft pull request, the non-slow tests are run. For pushes to main, the full test suite is run.

Also use my full name in the author section.

[Copilot]

Pull request overview

Adds GitHub Actions-based CI and introduces a slow pytest marker so computationally expensive tests can be excluded from default PR runs while still running on main.

Changes:

• Add @pytest.mark.slow usage and parameter-level slow marking for selected test systems.
• Register the slow marker in pytest config (pyproject.toml).
• Add a GitHub Actions workflow to run pytest -m "not slow" on non-draft PRs and full pytest on pushes to main.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 5 comments.

File	Description
tests/test_fci_systems.py	Adds slow-system classification and marks a larger-system CIPSI smoke test as slow.
pyproject.toml	Registers the slow pytest marker; also updates project author metadata.
.github/workflows/ci.yml	Introduces CI workflow for PR and main push testing with slow-test exclusion on PRs.

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