4d0a833e

By: ValentinHirschi <valentin.hirschi@gmail.com>

preserve completed contractions across tensor sums

Merge occurrence counts across alternative reconstruction branches while
retaining open-index reservations and incidence validation. Cover nested
closed sums, squared sums, shared external indices and factorized exact
canonicalization. Based on gammaloop's existing 0441bd7 dependency revision.

Validation: cargo check --lib --tests; nine tensor canonicalization tests pass.

User request:
OK, and make sure the fix to `Idenso reports a Lorentz dummy contracted more than once` is generic. We really need a robust and generic gammaloop.