[P] ibu-boost: a GBDT library where splits are *absolutely* rejected, not just relatively ranked[P]

I built a small gradient-boosted tree library based on the screening transform from "Screening Is Enough" (Nakanishi 2026, arXiv:2604.01178). The paper was originally written for Transformers, but the core idea — replacing relative comparison with absolute-threshold rejection — maps naturally onto G