Make build trace correctness validation sticky

What does this MR do?

This merge request aligns build trace correctness validation with how we roll live traces feature out.

We will only validate a build trace when associated build trace chunks are present. It does not make sense to validate traces of builds using traditional build logs architecture - partial checksums exist only for build trace chunks.

This is especially important during the incremental rollout, when we toggle a feature flag when builds are running.

Following screenshot describes the metric we want to optimize - we don't want to see invalid traces after switching a feature flag or adding new actors to the incremental rollout strategy.

Conformity

• Code review guidelines

/cc @marin @smcgivern