Code coverage report for translate tests

[FlorianDeconinck]

As of now we expect most code to be triggered by the translate test because we have carefully hand checked. Going forward and because there is code difference between what GEOS and SHiELD wants to run for the dycore (among other challenges) we need to have a system that make sure we cover all of our ported code with the translate tests.

This won't be 100% fault-proof since we still could run the code with inputs that don't trigger side-cases in the numerics that create issues, but it will help making sure we have a reasonable coverage, especially when regenerating translate test data.

Parent: https://github.com/GEOS-ESM/SMT-Nebulae/issues/41

---

• [ ] Introduce code coverage for translate tests
• [ ] Allow tuning of the "coverage" expected depending on what you are running, starting with all the code in pyFV3 when running the full set of tests
• [ ] Make sure the results of code coverage is easy to find, read and queryable for external tools.

[FlorianDeconinck]

ndsl unit test is code covered now by the coverage package.

--> https://github.com/NOAA-GFDL/NDSL/pull/40