Refactor task to avoid creating and swapping mix files on runs

[dariodf]

In order to avoid generating and overwriting files on the fly, this PR makes use of some undocumented Mix functions to change the Mix.Project configuration on a task runtime. With this possibility, we:

• Set up the mix lcov task to run a mix lcov.run subtask that runs recursively in the :test environment for each project.
• Make mix lcov.run change the current project configuration to add LcovEx as the :test_coverage tool, and run the actual mix test task for the project.
• Finish handling umbrella project stuff in the mix lcov task once the recursive tasks finished.

Also, some tests were updated to run with the proper configuration and increase the overall line coverage.

[paulswartz]

I tried this out on one of our Umbrella applications, and while it is creating the global .lcov, it looks like it's not correctly creating the file paths: https://github.com/paulswartz/api/actions/runs/3313439996

Here's the first couple lines of the .lcov file:

TN:Elixir.ALBMonitor
SF:lib/alb_monitor.ex

However, the actual file lives at apps/alb_monitor/lib/alb_monitor.ex.

Another issue (which might not be lcov_ex's fault) is that mocks using mox appear as a file within the deps module. I'm not sure what the right behavior is: probably ignoring them?

TN:Elixir.FakeAws
SF:/home/runner/work/api/api/deps/mox/lib/mox.ex

[dariodf]

Another issue (which might not be lcov_ex's fault) is that mocks using mox appear as a file within the deps module. I'm not sure what the right behavior is: probably ignoring them?

You are completely right, this happens when you add the mocks.ex file and the mock modules get compiled beforehand, and a simple ignored_paths: ["deps/"] default did the trick.

Would you mind giving it another round? Thank you very much again!