Parallelise o2dpg generator tests

[jackal1-66]

This PR enables parallel o2-sim* tests. With many configurations we were often hitting a timeout, and one of the causes is linked to the fact that we were testing sequentially each setting. The number of jobs is now set automatically using the JOBS environment variable (provided by the alidist recipe) and it's set to 8 by default.

[github-actions]

REQUEST FOR PRODUCTION RELEASES:
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[jackal1-66]

The Test with many generators commit will be reverted as soon as the CI is green (it's useful to test around 60 configurations on-the-fly)

[wuctlby]

A minor comment:
the flag fail immediately differs between comments/readme (fail**-**immediately) and code (fail**_**immediately).
https://github.com/jackal1-66/O2DPG/blob/907d77ee7382e9102907dbbf8860b15c67bd3086/test/run_generator_tests.sh#L361C49-L361C60

[jackal1-66]

Hello @wuctlby , please next time just review the code by clicking on "Files changed" and highlighting the line you want to comment.