fd5f846e

By: Kaapo Seppänen <seppanenkaapo@gmail.com>

fix dense tensor traces over several index pairs

Every pass after the first reused the original structure, data and trace
positions instead of the partially traced tensor, which panics or sets
components of the wrong structure. Locate each pair on the current result.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>