switch from PyQt6 to PySide6

PySide6 uses LGPL instead of GPL, which is much nicer to work with.

raven/mainwindow.py

@@ -1,9 +1,10 @@
 import logging
 from typing import List
 
-from PyQt6.QtWidgets import *
-from PyQt6.QtGui import *
-from PyQt6.QtCore import Qt
+from PySide6.QtWidgets import *
+from PySide6.QtGui import *
+from PySide6.QtCore import Qt
+
 import urlutils
 from cutesettings import CuteSettings
 from raven.pluginregistry import PluginRegistry