Configure testing suite

[nathanjmcdougall]

Motivation
Testing is a non-negotiable part of developing reliable software.

Summary of desired feature
A test suite and associated CI configuration set up for the project.

Design

• The tests will be run using pytest.
• The test suite will live in the tests directory.
• uv will be used to install pytest and manage dependencies.

Describe alternatives you've considered

• I haven't considered any other testing frameworks than pytest.
• I have found it interesting when working on pins-python that the tests folder was inside the package folder. This supports a more modular approach suitable for monorepos, but I don't think it's necessary for this project and quite unconventional.
• Managing dependencies could be done with rye. However, uv is already basically fit for purpose, even though its lockfiles etc. are quite experimental.

Testing Strategy
I would be able to see a successful CI pipeline which runs the testing suite.

Steps

• Configure the project with uv.
• Create a dummy test which just passes trivially.
• Confirm that pytest runs the test successfully from the CLI
• Set up GitHub actions CI pipeline to run pytest on multiple OSs.

Acceptance Criteria
The CI needs to be able to run at least one test.