Input JSON file for test ranges + weekly CI workflow

[PaulRBerg]

After #263 gets merged, let's add an input JSON file for defining test ranges, and modify the relevant tests like so:

1. If the JSON file is not present, apply the default ranges, i.e., the realistic ones that stream ~$100 per month.
2. Otherwise, load the ranges from the JSON file.

Then, add a new CI workflow that is scheduled to run on a weekly basis, which creates a JSON file with unrealistic test ranges.

This approach achieves the best of both worlds — focusing on realistic scenarios for the most part, but also proving that the protocol doesn't break when the payment rates are extreme.

[smol-ninja]

A relevant discussion: #296 (comment)