Remove SketchBlock operation in favor of a new Group type

[pierremtb]

Stacked on #10780.

Started as just a little fix but now pivoted to using the Group approach to deal with nested items under a sketch block.

[vercel]

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Project	Deployment	Actions	Updated (UTC)
modeling-app	Ready	Preview, Comment	Apr 8, 2026 4:14pm

[codspeed-hq]

Merging this PR will not alter performance

✅ 167 untouched benchmarks
⏩ 93 skipped benchmarks¹

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_{Comparing pierremtb/jtran-node-path (e7d8a23) with main (2b8de9f)²}

Footnotes

1. 93 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

2. No successful run was found on main (116b517) during the generation of this report, so 2b8de9f was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[jtran]

If it were me, I would delete this since the information is now in the GroupBegin and its Group. It makes it more similar to how function calls work.

[pierremtb]

Thank you!