Function std::webgpu_matmul

int webgpu_matmul(
    struct WebGpuBuf a,
    struct WebGpuBuf b,
    struct WebGpuBuf out,
    unsigned long M,
    unsigned long K,
    unsigned long N,
)

out [M, N] = a [M, K] . b [K, N], row-major. a and b share a dtype (fp32, fp16 or bf16; products accumulate in fp32), out is any dtype. Queued.