Function sync_and_check

tests/test_expanded_tensor_ops.cpp:10–15

using namespace lfs::core;

static cudaError_t sync_and_check() {
    cudaError_t err = cudaDeviceSynchronize();
    if (err != cudaSuccess)
        return err;
    return cudaGetLastError();
}

static void assert_cuda_ok(const char* step) {
    cudaError_t err = sync_and_check();