Add colors to subtests and small layout changes

[julienw]

This PR has 4 commits:

1. adds colors to the subtests view.
2. a small performance-related change about how we deal with the dark and light styles in the subtests page.
3. change how the grid's columns are configured -- instead of an hardcoded value, it comes from the cellsConfiguration. This makes it easier to do different adjustments in the subtests view vs the main view.
4. adjusts a little bit the layout of the results table so that the columns look more aligned.

I did all these changes here because without these changes, the color boxes in the subtests view was moving everything and this wasn't nice at all.

Production / Deploy preview

subtests page:

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After:

main page with no changes

Before:

After:

main page with improvements

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After:

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[codecov[bot]]

Codecov Report

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

Project coverage is 91.39%. Comparing base (9f6d734) to head (b9cd6bf). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #751 +/- ## ========================================== + Coverage 91.34% 91.39% +0.04% ========================================== Files 85 85 Lines 2242 2254 +12 Branches 423 427 +4 ========================================== + Hits 2048 2060 +12 Misses 171 171 Partials 23 23 ```

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