This commit adds the TreeNodeView class, a StatelessWidget responsible for rendering individual nodes in the skill tree.
Features:
- Displays the node ID in the view.
- Uses the Provider package to interact with the SkillTreeViewModel.
- Includes an onTap method to toggle node selection state.
- Updates the UI to reflect the selected state by changing the background color.
The TreeNodeView is designed to work in conjunction with SkillTreeViewModel to manage node selection states.
