perf: transpose-quantize backward operands to route all gemms nt
- quantize gains out_layout (0 row-major / 1 transposed / 2 single-read dual-write); modes 1/2 run a new 32x32 smem-tile transpose kernel
- backward feeds g8/w8T and g8T/x8T to trans_b=True gemms, dropping the NN-swap and TT crosswise kernels from training; fp8 weights keep the swap fallback
- a 64x64 tile variant tied on the real step mix and was reverted; noted in the kernel header
Benchmark: NVIDIA L20, 1.2B model, full train step fwd+bwd+CE
- M=8192: fp8 551.8 -> 532.2 ms, 1.21x -> 1.26x vs bf16; M=2048 0.90x -> 0.95x
- kernel-level grad_x +3.7..12.4%, grad_w +13.8..20.8%; layouts byte-exact, fp8 tests 36/36
ViperEkura
8a353117ea