Speed up build time using micromamba

[IAlibay]

Let's see how much time we can save (particularly on macos) by switching to micromamba.

In this PR:

• Improved build speeds by ~ 50% (although in practice only saves ~ 30-50s per runner total).
• Removed unecessary runners / moved them to Cron CI
• Add old ubuntu + macos scan to cron CI.

PR Checklist

• Tests?
• Docs?
• CHANGELOG updated?
• Issue raised/referenced?

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📚 Documentation preview 📚: https://readthedocs-preview--4121.org.readthedocs.build/en/4121/

[github-actions]

Linter Bot Results:

Hi @IAlibay! Thanks for making this PR. We linted your code and found the following:

There are currently no issues detected! 🎉

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (30baa14) 93.59% compared to head (6f2e50f) 93.59%.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #4121   +/-   ##
========================================
  Coverage    93.59%   93.59%           
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  Files          192      192           
  Lines        25134    25134           
  Branches      4056     4056           
========================================
  Hits         23524    23524           
  Misses        1092     1092           
  Partials       518      518           

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[hmacdope]

One question but other than that looks good and everything green.

[hmacdope]

Question what needs jaimergp/label/unsupported-cudatoolkit-shim?

[IAlibay]

OpenMM otherwise we're pulling down cuda everywhere. - it's quite widely used everywhere (in CI) nowadays

[hmacdope]

Cool beans