Habit tracker Bug Fix

Hello @bizz84 I saw your animation course on your website and I was fascinated by the habit tracking application. I went to your repository and forked it so I could test it on my physical android. I came across some runtime bugs.

So I decided to create a branch to solve these bugs.

The application works perfectly.

I hope this solution will benefit other students who will attend your course in the future. Thank you.

When running the habit tracker app with Flutter 2.10, the following error is thrown when flipping the page:

FlutterError (Duplicate GlobalKeys detected in widget tree.
The following GlobalKeys were specified multiple times in the widget tree. This will lead to parts of the widget tree being truncated unexpectedly, because the second time a key is seen, the previous instance is moved to the new location. The keys were:
- [LabeledGlobalKey<SlidingPanelAnimatorState>#2cd41 backSlidingPanelLeftAnimator]
  [LabeledGlobalKey<SlidingPanelAnimatorState>#a0a7a backSlidingPanelRightAnimator]
This was determined by noticing that after widgets with the above global keys were moved out of their respective previous parents, those previous parents never updated during this frame, meaning that they either did not update at all or updated before the widgets were moved, in either case implying that they still think that they should have a child with those global keys.
The specific parents that did not update after having one or more children forcibly removed due to GlobalKey reparenting are:
- Positioned(left: 0.0, bottom: 6.0, width: 54.0)
  Positioned(right: 0.0, bottom: 6.0, width: 336.0)
A GlobalKey can only be specified on one widget at a time in the widget tree.)

This will happen multiple times, and will also be followed by this:

FlutterError (Looking up a deactivated widget's ancestor is unsafe.
At this point the state of the widget's element tree is no longer stable.
To safely refer to a widget's ancestor in its dispose() method, save a reference to the ancestor by calling dependOnInheritedWidgetOfExactType() in the widget's didChangeDependencies() method.)

And this:

FlutterError (Duplicate GlobalKeys detected in widget tree.
The following GlobalKeys were specified multiple times in the widget tree. This will lead to parts of the widget tree being truncated unexpectedly, because the second time a key is seen, the previous instance is moved to the new location. The keys were:
- [LabeledGlobalKey<SlidingPanelAnimatorState>#5cb20 backSlidingPanelRightAnimator]
  [LabeledGlobalKey<TasksGridState>#7e5b1]
  [LabeledGlobalKey<SlidingPanelAnimatorState>#272dd frontSlidingPanelLeftAnimator]
  [LabeledGlobalKey<SlidingPanelAnimatorState>#c106a backSlidingPanelLeftAnimator]
  [LabeledGlobalKey<SlidingPanelAnimatorState>#b9fe3 frontSlidingPanelRightAnimator]
This was determined by noticing that after widgets with the above global keys were moved out of their respective previous parents, those previous parents never updated during this frame, meaning that they either did not update at all or updated before the widgets were moved, in either case implying that they still think that they should have a child with those global keys.
The specific parents that did not update after having one or more children forcibly removed due to GlobalKey reparenting are:
- Positioned(right: 0.0, bottom: 6.0, width: 336.0) (2 different affected elements had this toString representation)
  Positioned(left: 0.0, bottom: 6.0, width: 54.0) (2 different affected elements had this toString representation)
  Padding(padding: EdgeInsets(24.0, 16.0, 24.0, 16.0), dependencies: [Directionality], renderObject: RenderPadding#7e3e9 relayoutBoundary=up4 NEEDS-LAYOUT NEEDS-COMPOSITING-BITS-UPDATE DETACHED)
A GlobalKey can only be specified on one widget at a time in the widget tree.)