title: Pandas datetime results are different after substract
body: <p>I have a following simple piece of code:</p>
  
  <pre><code>pd.to_timedelta(
    pd.to_datetime("2020-05-03 19:12:39.406636238") - pd.to_datetime("2020-05-03 19:12:36.508889914")
    )
  )
  # Result = 00:00:02.897746 
  </code></pre>
  
  <p>Looks like, this result is trimmed a bit.</p>
  
  <pre><code>pd.to_datetime("2020-05-03 19:12:36.508889914") + pd.to_timedelta("00:00:02.897746"))
  # Result = 2020-05-03 19:12:39.406635914
  </code></pre>
  
  <p><strong>2020-05-03 19:12:39.406636238 != 2020-05-03 19:12:39.406635914</strong></p>
  
  <p>Why the results are different? Can I control the digits after comma for timedelta? </p>