tests: add basic test for common methods

[daywalker90]

The plugin repo will require plugins to have tests in the future. So here is a basic test for

• circular
• circular-pull
• circular-push
• circular-stats

Unfortunately i could not get circular-push to work. You can see the error here: https://github.com/daywalker90/plugins/actions/runs/8782156065/job/24095700451#step:8:822

To run tests yourself:

pip3 install pyln-client pyln-testing
git clone https://github.com/giovannizotta/circular
cd circular/tests
./setup.sh # or provide the circular binary yourself inside the tests folder
cd ..
pytest tests/test_circular.py # or pytest -o log_cli=true --log-cli-level=INFO tests/test_circular to enable logging output

[giovannizotta]

Thanks a lot for your contribution! I will merge as-is, since the plugin repo considers the absence of test as much as a failure as a failing test. Let's investigate the issue with circular-push separately to not block this PR, as discussed