The more aggressive matmul kernel lost to the register budget

The WebGPU matmul sweep started with a naive kernel, then added 16 by 16 workgroup tiling and a 4 by 4 output block per thread. At a 2048 cubed matrix size, the measured time moved from 47.24 ms for the naive kernel to 17.23 ms for tiling and 9.12 ms for the 4 by 4 blocked kernel. The blocked version was 5.18 times faster than naive at that size....