[WIP] Experiment with pixi for CI

[hadim]

Changelogs

• enumerate the changes of that PR.

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Checklist:

• [ ] Was this PR discussed in an issue? It is recommended to first discuss a new feature into a GitHub issue before opening a PR.
• [ ] Add tests to cover the fixed bug(s) or the new introduced feature(s) (if appropriate).
• [ ] Update the API documentation is a new function is added, or an existing one is deleted.
• [ ] Write concise and explanatory changelogs below.
• [ ] If possible, assign one of the following labels to the PR: feature, fix or test (or ask a maintainer to do it for you).

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This is an experiment to try to understand two things: 1) whether pixi can be a faster alternative than micromamba 2) whether it's mature enough and has enough features for us (matrix testing)

[codecov[bot]]

Codecov Report

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

Comparison is base (c23d273) 91.95% compared to head (1143cbd) 91.90%. Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #218 +/- ## ========================================== - Coverage 91.95% 91.90% -0.06% ========================================== Files 46 46 Lines 3843 3843 ========================================== - Hits 3534 3532 -2 - Misses 309 311 +2 ``` | [Flag](https://app.codecov.io/gh/datamol-io/datamol/pull/218/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=datamol-io) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/datamol-io/datamol/pull/218/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=datamol-io) | `91.90% <ø> (-0.06%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=datamol-io#carryforward-flags-in-the-pull-request-comment) to find out more.

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[hadim]

I will close here.

In short, pixi CI is not really faster than the current micromamba one. It's expected since micromamba is already quite fast and the current bottlenecks are things we can't control: 1) deps downloading and extracting or 2) cache downloading and extracting.

Finally, matrix CIs is possible but a bit hacky currently (see https://github.com/Quantco/polarify/blob/dcc30139873c4aa7500465e116b6f9f6194b77b3/.github/workflows/ci.yml#L19-L40). That being said, it will very soon be much easier (see https://github.com/prefix-dev/pixi/issues/239).

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TLDR: I foresee a bright future for the pixi tool, but for now, it does not make sense to switch datamol to it.