ReadonlyfusedReadonlykReadonlyvDecode a TurboQuantTensor's active [B,H,upTo,*] window back to bf16 [B,H,upTo,headDim] (k, v). Caller owns the returned arrays. deferV leaves V in the rotated domain (decodeValuesRotated) — the caller un-rotates its attention output instead (tq.unrotateValues).
Encode k/v [B,H,L,D] into a fresh TurboQuantTensor (packed at rest).
Numerical representation only. Storage owns capacity, positions, row membership and persistence; this codec retains the existing kernel choices.