gh-104584: Handle EXTENDED_ARG in superblock creation

[gvanrossum]

Also fixed and cleaned up test_capi.test_misc.TestUops, and added a new test proving that EXTENDED_ARG works.

• Issue: Pluggable optimizer API #104584

[gvanrossum]

Tests are failing. I'll regroup and see if my EXTENDED_ARG handling is at fault or if it was pre-existing, and then proceed from there. For now, this is another Draft PR, and I'll isolate my test cleanups in a new PR.

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UPDATE: Fixed by gh-106492, rebased, undrafted.

[gvanrossum]

I get the same failure with just Fix and clean up uops and executor API. That makes me think the root problem is pre-existing (since that commit has no C code). I'll see if the address sanitizer will help me debug this.

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UPDATE: Yeah, the UOpOptimizer type was missing a tp_dealloc handler. Nasty. Fixing that in gh-106492. Once that's merged I'll rebase and undraft this.