title: How to import QGIS widgets into pyqt6 app?
body: <p>I've downloaded OSGeo4W and using Qt designer I've made my app, adding QgsCheckableComboBox components into it. (with some other base Qt widgets)
  I then saved .ui file and transferred it into .py with command
  <code>pyuic6 -x test.ui -o test.py</code>. The generated file is perfectly fine, but I have an import which I cannot resolve:</p>
  <p><code>from qgscheckablecombobox import QgsCheckableComboBox</code></p>
  <p>getting an error:
  <code>ModuleNotFoundError: No module named 'qgscheckablecombobox</code>
  How am I supposed to import QGIS widgets into PyQt6 ?
  How do I add it to path?</p>
  <p>P.S.
  All of this code was generated using Qt designer:
  <a href="https://i.stack.imgur.com/Vayvi.png" rel="nofollow noreferrer">photo inside qt designer</a></p>
  <p><a href="https://i.stack.imgur.com/9pp0P.png" rel="nofollow noreferrer">preview from qt designer</a></p>