_fast_ce/_shifted_ce were renamed to _fast_lin_ce/_shifted_lin_ce and changed
from logits-based to Liger fused-linear-CE (hidden @ lm_head_weightᵀ). Update
the tests via thin adapters that pass an identity lm_head_weight (so the
computed logits equal the provided ones), run on CUDA (Liger is GPU-only) and
skip otherwise, and loosen the allclose tolerance to absorb GPU-vs-CPU float
noise on the tiny losses.
Co-authored-by: Cursor <cursoragent@cursor.com>