Add CI to run the unit test suite on pull requests

[dmccoystephenson]

Context

PR #10 introduces this repository's first automated tests, in tests/test_render_window.py. They are pure unittest tests that mock Pygame, so they need neither a display nor a running Viron server, and they complete in well under a second.

No .github/workflows/ directory exists, so nothing runs them automatically. Every future change would rely on a reviewer remembering to run python -m unittest discover -s tests by hand.

Proposal

A GitHub Actions workflow should be added that runs on pull requests targeting main and executes:

python -m unittest discover -s tests

Notes for whoever implements this:

• actions/checkout should be configured without submodules. The Viron submodule is only needed by main.py at runtime; the test suite does not import it, and cloning it would slow the job down for no benefit.
• README.md states a prerequisite of Python 3.10+, so the workflow's Python version should be pinned at or above that. Note that the current test suite itself uses only the standard library and runs on older interpreters as well.
• Pygame is imported by render_window.py, so pip install pygame is required even though the tests patch it out.
• A syntax check over the entry points (python -m py_compile main.py graphik.py __init__.py render_window.py render_window_example.py) would be a cheap addition to the same job, since neither main.py nor the example file is covered by tests.

Note

Adding a workflow modifies .github/workflows/, which is excluded from autonomous merge, so this is expected to be implemented and merged with human review.

This issue body was drafted during a Gardener session (https://github.com/Stephenson-Software/gardener).

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drafted by Claude on behalf of Daniel Stephenson