more tests and CI

[daywalker90]

Hi, awesome project you have here.

I'd like to contribute some tests and CI.

This PR adds 3 more tests:

• test_general_prism: general test of almost all plugin methods and a full prism pay test
• test_splits: test a non-equal split
• test_payment_threshold: test payment thresholds (currently failing!)

I didn't dig into the code to find out why payment_threshold doesn't work, because there was a TODO above payment_threshold.

I also added a CI that runs these tests against CLN 24.02.2 on every PR and commit to main and included a badge that will show the latest run status of a commit to the main branch (not PR's).

[farscapian]

Hi @daywalker90 , excited to have you as a contributor. The payment_threshold issue should be fixed on the https://github.com/gudnuf/bolt12-prism/tree/btcpp24 branch, as well as prism-show in the docs. I'll be submitting a PR after some additional testing.

Extremely happy to get your help on the test cases and CI workflow! Definitely an area we need to improve!