return Sc::zero() for unchanged

[NewBornRustacean]

Hello @blackopsrepl 😃
I was looking into the scoring side today and found a place where an early return seemed useful.

1. Changes
   Add an early return in IncrementalCrossBiConstraint::on_insert when the changed descriptor does not affect either a and b. This avoids calling extractor_a.extract(solution) and extractor_b.extract(solution) for unrelated descriptor changes.

2. Expected Impact
   Reduces unnecessary work in the incremental scoring hot path during local search candidate evaluation. This should help multi-descriptor problems with multiple constraints, where many entity changes may be irrelevant to a given cross-bi constraint.

[blackopsrepl]

Hey @NewBornRustacean, good point!

These days I was refactoring the codebase for smaller LOC per file, but didn't push it here, yet.

The code you fixed is now in:
crates/solverforge-scoring/src/constraint/cross_bi_incremental/incremental.rs

I think it's easier if you submit a new PR to the updated main branch, so you don't lose commit history. Will be happy to merge immediately.
If we could also include a minimal test proving unrelated on_insert does not call the extractors, then even better!

Closing this one - thank you!

[NewBornRustacean]

yebb 👍 will open a new one with proper tests!