Prevent tests from altering user config/preferences

TODO; prevent tests from altering user settings

Add to top conftest something like:
```
_settings_dir = Path(tempfile.gettempdir()) / (...)
_settings_dir.mkdir(parents=True, exist_ok=True)
QSettings.setDefaultFormat(QSettings.Format.IniFormat)  # because of Win registry
QSettings.setPath(QSettings.Format.IniFormat, QSettings.Scope.UserScope, str(_settings_dir))
```