Nightly build with cython coverage enabled

[jbrockmendel]

xref #25529

[jbrockmendel]

@TomAugspurger any idea what it would take to do this on the dev machine?

[TomAugspurger]

I'd rather have these on a CI service like azure or Travis if possible (don't we have a longer timeout for Azure?).

Azure calls these "scheduled builds" and they can be configured through the web UI only right now. If you create an account for Azure I'll add you to the team.

[jbrockmendel]

If you create an account for Azure I'll add you to the team.

I think I've got an Azure account, should have the same name as my GH account