Run US and UK calibration as GitHub actions

[nikhilwoodruff]

By this, we mean that every week, this repo should run the calibration routine on the latest version of the country packages, update the weights as a pandas CSV for each country in a data release on this repo, and run pytest tests that ensure:

• No negative weights
• Effective sample size (number of nonzero records) is larger than 10k
• Loss is reduced

[nikhilwoodruff]

https://docs.github.com/en/actions/using-workflows/events-that-trigger-workflows