Convert PEP 630 (Isolating Extension Modules) to "HOWTO"

[encukou]

As per PEP-687, the informational PEP-630 is moved to the docs as a HOWTO.
It's not really a Diátaxis-style How-to guide -- it's more of an Explanation with instructions thrown in. I'm not sure how to split it without spending weeks on it. (FWIW I think the time I can dedicate to this would be better spent on the Tutorial.)

@python/proofreaders, suggestions welcome – anything from typo fixes to complete restructuring :)

[AlexWaygood]

I skim-read, but here's a few small comments!

[bskinn]

I read the whole thing to orient myself. I'll have comments and suggestions, once I have a chance to write them out. End of day Monday at latest, I think.

[CAM-Gerlach]

Likewise, I've read it, but due to the length I'll need to save my full review comments for another day, hopefully tomorrow.

[bskinn]

High level question: who is the target audience? Only experienced C extension developers? Experienced and learning Cext developers?

Where is this document going to be referred to, elsewhere in the docs, and who is that likely to draw to the page?

Right now this feels written only toward experienced extension developers. This is fine, if that's the goal!

But IMO the audience should be stated up front. And, if possible, links to other resources for people who aren't the target audience should be provided. (If the audience is experienced extension devs, say, then link(s) to getting-started resources for C extensions.)

[encukou]

who is the target audience?

Yes, experienced extension developers – ones currently maintaining extensions.
I'm painfully aware we don't currently have docs to onboard people to this level. My longer-term plan is to change the extending/embedding tutorial to guide peuple to a point where they don't need a “how to switch to the new way” guide.

[ambv]

This is awesome. Let's have it as is and backport to 3.11 as well. We can iterate on the content after.

[miss-islington]

Thanks @encukou for the PR, and @ambv for merging it 🌮🎉.. I'm working now to backport this PR to: 3.11.
🐍🍒⛏🤖

[bedevere-bot]

GH-94566 is a backport of this pull request to the 3.11 branch.