Terminate dev test processes with prejudice on exit

[GregBrimble]

Fixes #397 (and #618)

Kills the dev processes aggressively when jest is finished its tests of the example repos.

Seems a handy utility. Maybe we use it elsewhere as well?

[threepointone]

Is there a solution where we actually clean up correctly instead of doing this? What is the source of the hanging processes/ports?

[threepointone]

might be related #543

[GregBrimble]

#543 is what I was hinting at where we could use this elsewhere. Inside the pages dev command, we spin up a couple of processes, and we certainly do try to clean them up on exit. But this utility might be doing a better job than I can. So maybe we swap out my logic in that command for this as well?

[threepointone]

I really don't want us to install a non trivial dependency for something that seems like we should be getting right. Can we investigate why we're struggling to close this process at all, if you're saying we already have code to do so?

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[petebacondarwin]

Why did the CI not run?

[petebacondarwin]

I don't think this needs to be here, right?

[threepointone]

GitHub actions (and other GitHub services) was having problems yesterday

[threepointone]

Could we resolve this soon-ish please? It's starting to affect builds in CI now too

[GregBrimble]

New PR up in #670