code: def test_zero_copy_from_default_to_cpu(self):
      demo = Tensor.rand(1).realize()
      t1 = time_tensor_numpy(demo)
      out = Tensor.rand(N, N).realize()
      t2 = time_tensor_numpy(out)
      gbps = out.nbytes() * 1e-9 / max(t2 - t1, 1e-10)
      print(
          f"time(base): {t1*1e3:.2f} ms, time(copy): {t2*1e3:.2f} ms :  copy speed {gbps:.2f} GB/s"
      )
      self.assertGreater(gbps, 600)
  
imports: import unittest
  from tinygrad import Tensor, Device
  import time
label_desc: Use image node_id 1 for calling the TestZeroCopy obj's underlying member method code with example usage: obj.test_zero_copy_from_default_to_cpu() without return types