blockscaled_chunk_kmajor packed words are byte-identical to the
CUTLASS/CuTeDSL canonical blocked SF layout (tile_atom_to_shape_SF,
sf_vec_size=16, atom ((32,4),(16,4)):((16,4),(0,1)) tiled with order
(2,1,3)); the two views bridge zero-copy via torch view casts. Document
that on the packer and lock it with a cross-layout contract test.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>