TruthMetrics

What the candidate got wrong, per frame (§RQ-4.2).

In the namespace raybench. Declared in src/libs/libraybench/raybench/GroundTruth.hpp.

Detailed description

The two mask fractions are separated on purpose: `tunneled` (truth says surface, candidate says empty) is a correctness failure — the ray walked through the model — while `bloated` (candidate says surface, truth says empty) is a silhouette that grew, which looks fine in a screenshot and ruins a measurement.