Function on_enter_node 

pub fn on_enter_node(
    e: On<'_, '_, PointerEnter>,
    virtual_s: Option<Single<'_, '_, (&mut VirtualSegment, &Transform, &mut Mesh2d), Without<VirtualNode>>>,
    virtual_n: Single<'_, '_, &mut Transform, With<VirtualNode>>,
    q_nodes: Query<'_, '_, (&Transform, &mut MeshMaterial2d<ColorMaterial>), (With<TrackNode>, Without<VirtualNode>)>,
    from_node_type: ResMut<'_, FromNodeType>,
    meshes: ResMut<'_, Assets<Mesh>>,
    assets_manager: Res<'_, AssetsManager>,
)

Observer responding to the user entering their pointer to a node and responding accordingly, changing either the from or to nodes to physical ones.