Fix widget flashing on init by properly parenting (#95)

# References and relevant issues

Depends on #94

Here is the diff
TimMonko/napari-metadata@mnt/proj-reorg...TimMonko:napari-metadata:fix/widget-flash

# Description

This passes the parent to the collapsible widgets so that they do not
briefly flash before being docked in the main container. Tested locally
with napari.

Author: TimMonko

src/napari_metadata/widgets/_containers.py

@@ -44,7 +44,7 @@ def __init__(
         main_widget: MetadataWidgetAPI,
         orientation: Literal['vertical', 'horizontal'] = 'vertical',
     ):
-        super().__init__()
+        super().__init__(parent=main_widget)
         self._viewer = viewer
         self._container_name = container_name
         self._main_widget = main_widget
@@ -72,7 +72,7 @@ def __init__(
         self._layout.addWidget(self._button, 0)
 
         # Create expanding area
-        self._expanding_area = QScrollArea()
+        self._expanding_area = QScrollArea(self)
         self._expanding_area.setWidgetResizable(True)
 
         if orientation == 'vertical':
@@ -191,7 +191,7 @@ def _set_expanding_area_widget(self, setting_widget: QWidget) -> None:
             self._expanding_area.setWidget(setting_widget)
         else:  # horizontal
             # Horizontal containers need a wrapper with stretch
-            wrapper = QWidget()
+            wrapper = QWidget(self._expanding_area)
             wrapper_layout = QVBoxLayout(wrapper)
             wrapper_layout.setContentsMargins(0, 0, 0, 0)
             wrapper_layout.addWidget(setting_widget)

src/napari_metadata/widgets/_main.py

@@ -103,25 +103,25 @@ def __init__(self, napari_viewer: 'ViewerModel'):
         )
         self._connect_file_general_metadata_components()
 
-        self._vert_file_general_metadata_container: QWidget = QWidget()
+        self._vert_file_general_metadata_container: QWidget = QWidget(self)
         self._vert_file_general_metadata_layout: QGridLayout = QGridLayout()
         self._vert_file_general_metadata_container.setLayout(
             self._vert_file_general_metadata_layout
         )
-        self._hori_file_general_metadata_container: QWidget = QWidget()
+        self._hori_file_general_metadata_container: QWidget = QWidget(self)
         self._hori_file_general_metadata_layout: QGridLayout = QGridLayout()
         self._hori_file_general_metadata_container.setLayout(
             self._hori_file_general_metadata_layout
         )
 
         self._axis_metadata_instance = AxisMetadata(napari_viewer, self)
 
-        self._vert_axis_metadata_container: QWidget = QWidget()
+        self._vert_axis_metadata_container: QWidget = QWidget(self)
         self._vert_axis_metadata_layout: QGridLayout = QGridLayout()
         self._vert_axis_metadata_container.setLayout(
             self._vert_axis_metadata_layout
         )
-        self._hori_axis_metadata_container: QWidget = QWidget()
+        self._hori_axis_metadata_container: QWidget = QWidget(self)
         self._hori_axis_metadata_layout: QGridLayout = QGridLayout()
         self._hori_axis_metadata_container.setLayout(
             self._hori_axis_metadata_layout
@@ -132,25 +132,25 @@ def __init__(self, napari_viewer: 'ViewerModel'):
             napari_viewer, self
         )
 
-        self._vert_inheritance_container: QWidget = QWidget()
+        self._vert_inheritance_container: QWidget = QWidget(self)
         self._vert_inhertiance_layout: QGridLayout = QGridLayout()
         self._vert_inheritance_container.setLayout(
             self._vert_inhertiance_layout
         )
-        self._hori_inheritance_container: QWidget = QWidget()
+        self._hori_inheritance_container: QWidget = QWidget(self)
         self._hori_inheritance_layout: QGridLayout = QGridLayout()
         self._hori_inheritance_container.setLayout(
             self._hori_inheritance_layout
         )
 
-        vertical_container: QScrollArea = QScrollArea()
+        vertical_container: QScrollArea = QScrollArea(self)
         vertical_container.setWidgetResizable(True)
         vertical_container.setHorizontalScrollBarPolicy(
             Qt.ScrollBarPolicy.ScrollBarAlwaysOff
         )
         vertical_container.container_orientation = 'vertical'
 
-        vertical_content = QWidget()
+        vertical_content = QWidget(vertical_container)
         vertical_content.setLayout(self._vertical_layout)
         vertical_container.setWidget(vertical_content)
 
@@ -208,7 +208,7 @@ def __init__(self, napari_viewer: 'ViewerModel'):
         self._vertical_layout.addStretch(1)
 
         horizontal_container: HorizontalOnlyOuterScrollArea = (
-            HorizontalOnlyOuterScrollArea()
+            HorizontalOnlyOuterScrollArea(self)
         )
         horizontal_container.setWidgetResizable(True)
         horizontal_container.setVerticalScrollBarPolicy(
@@ -219,7 +219,7 @@ def __init__(self, napari_viewer: 'ViewerModel'):
         )
         horizontal_container.container_orientation = 'horizontal'
 
-        horizontal_content: QWidget = QWidget()
+        horizontal_content: QWidget = QWidget(horizontal_container)
         horizontal_content.setLayout(self._horizontal_layout)
         horizontal_container.setWidget(horizontal_content)
         self._stacked_layout.addWidget(horizontal_container)
@@ -274,7 +274,7 @@ def __init__(self, napari_viewer: 'ViewerModel'):
         )
         self._horizontal_layout.addStretch(1)
 
-        no_layer_container: QWidget = QWidget()
+        no_layer_container: QWidget = QWidget(self)
         no_layer_container.container_orientation = 'no_layer'
         no_layer_container.setLayout(self._no_layer_layout)
         self._no_layer_label: QLabel = QLabel(