[WIP][ENH] Fix coverage for multiprocessed functions

[arnaudbore]

Quick description

Codecov is not covering multiprocessing functions. https://app.codecov.io/gh/scilus/scilpy/blob/master/scilpy%2Freconst%2Fdivide.py#L266 ...

Type of change

Check the relevant options.

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update

Provide data, screenshots, command line to test (if relevant)

...

Checklist

• [ ] My code follows the style guidelines of this project (run autopep8)
• [ ] I added relevant citations to scripts, modules and functions docstrings and descriptions
• [ ] I have performed a self-review of my code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [ ] My changes generate no new warnings
• [ ] I moved all functions from the script file (except the argparser and main) to scilpy modules
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] New and existing unit tests pass locally with my changes

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 69.17%. Comparing base (4c2848c) to head (de0060a). Report is 124 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #927 +/- ## ======================================= Coverage 69.17% 69.17% ======================================= Files 389 389 Lines 20963 20963 Branches 3233 3233 ======================================= Hits 14501 14501 Misses 5132 5132 Partials 1330 1330 ``` | [Components](https://app.codecov.io/gh/scilus/scilpy/pull/927/components?src=pr&el=components&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scilus) | Coverage Δ | | |---|---|---| | [Scripts](https://app.codecov.io/gh/scilus/scilpy/pull/927/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scilus) | `71.60% <ø> (ø)` | | | [Library](https://app.codecov.io/gh/scilus/scilpy/pull/927/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scilus) | `65.05% <ø> (ø)` | |