Reuse CI workflows across the workspace

[jschneider-bensch]

No description provided.

[franziskuskiefer]

I created cryspen/actions for general workflows. #335 is a first use of that.
Let's add generally useful workflows there.

[github-actions]

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[jschneider-bensch]

We should keep this open, since I can think of a number of tasks that could be used across different crates in the workspace (beyond even), e.g. a default setup & build or a build of a portable version of some crate, or setting up hax and extracting.