[OnFreund]

Why

There was no CI for tests. The only workflow, publish.yml, built and uploaded to PyPI on a version bump without running the test suite. The test dependencies (pytest, pytest-asyncio) also weren't declared anywhere, so a plain pip install -e . followed by pytest didn't work.

Changes

• .github/workflows/test.yml (new): runs pytest on the latest stable Python (3.x) for every pull request and every push to main. It also has a workflow_call trigger so other workflows can reuse it.
• publish.yml: adds a test job that calls test.yml. The publish job now has needs: test, so a failing test blocks the release.
• pyproject.toml: adds a test optional-dependency extra listing pytest>=8.0 and pytest-asyncio>=0.23.
• README: the development setup now uses pip install -e ".[test]".

Notes for reviewers

• In publish.yml, the tests now run on every push to main that changes pyproject.toml, even when the version didn't change and nothing gets published. That costs a little CI time but avoids complicating the workflow.
• Testing: all 25 tests on main pass in a fresh virtualenv set up with only pip install -e ".[test]". This PR's own checks should be the first real run of the workflow.
• Once this merges, Include MTA Bus Company static GTFS feed for bus routes #15 will get test runs too after it's rebased or updated.

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