title: Concatenate each element in a nested list with all elements in another nested list
body: <p>Given the 2 nested lists below where length of list1 could be &gt; length of list2 and vice versa.</p>
  <p>I want to add every elements in list1 with all other elements in list2.</p>
  <pre><code>List1 = [ 
        [2, 1],
        [1, 8]
      ]
  
  
  List2 = [ 
        [1,2],
        [4,5],
        [2,6],
        [7,9]
      ]
  </code></pre>
  <p><strong>----- Desired Results-----</strong></p>
  <pre><code>Result = [
        
        [2,1,1,2],
        [2,1,4,5],
        [2,1,2,6],
        [2,1,7,9],
        [1,8,1,2],
        [1,8,4,5],
        [1,8,2,6],
        [1,8,7,9]
       ]
  </code></pre>
  <p>My attempt below didn't give the results:
  Note: The len of each nested list is large and len of either list could be greater than the other.</p>
  <pre><code>import numpy as np
  
  res = [(i+j).to_list() for i, j in zip(list1, list2)]
  </code></pre>