:bug: Ensure output file path is always absolute
Improve specs and execute them using real `LatexmkBuilder`

* Once again running specs using a real `Builder` implementation to verify
  that everything works when running against `latexmk` and not just a
  Happy Path™ mock builder.
* Makes sure all specs are properly handling the async nature of `latex::build`.
* Also removes invokation status variables in favor of `callCount` checking
  on the spies.
Add test case that verifies log parsing end-to-end