refactor(test): heavily simplify the `context` helper

[agilgur5]

~NOTE: this is built on top of #397 as that also uses the context helper. It may also merge conflict with #396 if that is merged. As such, I've marked this PR as "Draft" until those PRs are merged (or otherwise closed).~ Rebased on top, fixed merge conflicts, and marked as ready for review.

Summary

Significantly simplify the context helper used in the unit tests with more forceful type-casting and directly using Jest mocks. This makes all usage of context significantly easier and less hacky, as can be seen in the changed tests here.

• Follow-up to #321 / #135

Details

• since we're type-casting it anyway, we can heavily simplify this and remove the stubs entirely

  • they're actually unused in the unit tests, so we don't need them at all
  • besides the type-checking, which we force with a cast anyway
  • the as unknown as is bad practice, and probably why I didn't use it initially (plus other typing issues), but it's much simpler this way and reflects the intent better -- just making it type-check with the few properties we use

• we can also use Jest mocks directly instead of the hacky contextualLogger and passing data in

  • makeContext now creates the mocks, so we just need to check against context.error etc
  • this is much more familiar as it's what we use in the source and follows idiomatic Jest
  • rewrite all the checks to test against the mocks instead
  • I thought this felt too complicated / verbose before, but I had left this as is from brekk's initial test structure
  • now that I understand all the tests and test intent much better, I could rewrite this to be a good bit simpler

• make the toBeFalsy() checks more precise by checking that the mock wasn't called

  • it returns void anyway, so toBeFalsy() always returns true; it's not much of a test
  • checking that the low verbosity level didn't trigger the mock to be called actually checks the test's intent