fix: packed FP4 for mxf4nvf4 — correct SMEM layout, UMMA descriptors, L1 epilogue
Key changes:
- a_dtype_t/b_dtype_t: float_e2m1_t (packed 4-bit) with sizeof_bits_v==4 assert
- kSwizzleAMode/BMode: BLOCK_K/2 (64 bytes packed, not 128 unpacked)
- SMEM sizes: LOAD_BLOCK_M * BLOCK_K / 2 (packed byte count)
- Token layouts: kHidden/2, kIntermediateHidden/2 (packed bytes)
- TMA loads: BLOCK_K/2 inner dim, uint8_t, byte offsets k_block_idx*(BLOCK_K/2)
- UMMA descriptors: BLOCK_K/2 template param, uint8_t dtype, UMMA_K/2 advance
- L1 epilogue: dropped STSM, direct st.shared.u16 with packed nibbles, no swizzle (v1)
- Pybind buffer sizes: hidden/2, intermediate_hidden/2 with packed tensor shapes
- Host TMA descriptors: hidden/2 K-dims, block_k/2 inner, fp4_unpacked_smem=false
- L1 output TMA: block_n/4 inner, no swizzle (CU_TENSOR_MAP_SWIZZLE_NONE)
biondizzle
30d72e7ef5