simplify code

[haesleinhuepf]

This block in _orthogonal.py could be simplified:

        widgets[0].viewer.observe(redraw0)
        widgets[0].viewer.observe(redraw1)
        widgets[0].viewer.observe(redraw2)

        widgets[1].viewer.observe(redraw0)
        widgets[1].viewer.observe(redraw1)
        widgets[1].viewer.observe(redraw2)

        widgets[2].viewer.observe(redraw0)
        widgets[2].viewer.observe(redraw1)
        widgets[2].viewer.observe(redraw2)

git-bob think about this!

[github-actions]

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for widget in widgets:
    widget.viewer.observe(redraw0)
    widget.viewer.observe(redraw1)
    widget.viewer.observe(redraw2)