gh-103583: Isolate CJK codec modules

[erlend-aasland]

• Issue: Isolate _multibytecodec #103583

[erlend-aasland]

This approach exploits the dependency introduced in gh-103589; we know for sure that the _codec* extension modules will outlive _multibytecodec. This means we can store the cjk codec module state safely in the codec struct and modify the various codec handlers to accept the codec struct (iso. void *config). Then we add custom cjk module state where needed, and conveniently fetch it from the codec struct. (Quick and dirty explanation; see the code if what I wrote does not make sense 😎)

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @erlend-aasland for commit ef983c4 🤖

If you want to schedule another build, you need to add the 🔨 test-with-refleak-buildbots label again.

[erlend-aasland]

BTW, I removed the initialized guards. I'm pretty sure we can do that, but I haven't verified it yet.

[erlend-aasland]

Also, we can split out cb2c9e7 as a separate PR. That may be beneficial regarding to future bisects; it will also make this PR easier to review.

Similarly, f6ed5df can be split up to do the arg spec changes first, and then move stuff to module state afterwards.

[erlend-aasland]

@vstinner, you want to take a look? :)

[corona10]

@erlend-aasland I will take a look by tomorrow

[erlend-aasland]

(Pulling in main to get the latest ref. leak fixes by Jelle)

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @erlend-aasland for commit dec79a7 🤖

If you want to schedule another build, you need to add the 🔨 test-with-refleak-buildbots label again.

[corona10]

LGTM, This is quite a complicated but nice approach. But nothing can be better than this.
Thanks for the hard work!

[erlend-aasland]

Thanks for the review, Dong-hee! Yes, it is complicated, but as shown in my competing PRs, other approaches are even more complicated.

[vstinner]

Well done @erlend-aasland!

[erlend-aasland]

Well done @erlend-aasland!

Thanks, Victor :) This was a tricky one!