text: Title: [BUG] AttributeError: 'series' object has no attribute 'array' when calling np.array(df)
  Body: ### Describe the bug
  When calling `np.array(df)` in my code, I encountered the following error: "`AttributeError: 'series' object has no attribute '__array__'`".
  
  ### To Reproduce
  To help us to reproduce this bug, please provide information below:
  
  1. Your Python version: python 3.8
  2. The version of Xorbits you use: the latest, 0.2.0
  3. Versions of crucial packages:
  numpy==1.22.4
  5. Minimized code to reproduce the error.
  
  ```
  import numpy as np
  import xorbits.pandas as pd
  
  # code that triggers the error
  data = np.array(df)
  ```
  
  
  ### Expected behavior
  I expected the `np.array()` function to create a numpy array from the Pandas DataFrame `df`.
  
  ### Additional context
  N/A
  