chore: get tests running in CI

[dbjorge]

While I was looking at making a different contribution, I noticed that the repo's tests weren't in a running state. It looks like the tests were written prior to the project converting to "type": "module", but the tests were never updated to work with that. This PR:

• Replaces jenkins-mocha and nyc with mocha and c8 to re-enable debugging and code coverage
• Updates the tests to use ESM syntax instead of CJS syntax
• Updates how packages-test.js was using child_process.spawn to fix how it was trying to read stdout
• Updates test.ts cases that pin to the actual dependencies of the repo to account for the dependency updates
• Adds a GitHub Actions configuration to run lint + format + test checks on PRs