Per review feedback on #7063. The two functions share the conds-by-hooks
accumulation, memory-fit batching, and per-chunk output aggregation; the
multigpu variant adds per-device scheduling, .to(device) placement,
per-device patcher/control lookup, and thread-pool dispatch around the
inner loop. Documenting the relationship without extracting helpers --
extraction can land after the initial worksplit-multigpu release once
both paths have settled.
Amp-Thread-ID: https://ampcode.com/threads/T-019e4a00-fe3d-76bd-a2f2-a8c8c4040082
Co-authored-by: Amp <amp@ampcode.com>
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