INT8ConvRot GEMM vs fp16 on M1 Max with Metal, MPSMatrix, and MLX (fp16 Wins)

Measured on M1 Max 64GB: weight-only INT8 runs 41% slower than fp16, a hand-written Metal int8 GEMM 15.6x slower, MPSMatrix int8 3x, and MLX 8-bit 9% slower.