Fix: Add dummy widgets to suppress NameError and warn about missing ipywidgets

[mrapacz]

This addresses #3755

Resolution

This PR fixes the issue by defining dummy FloatSlider and IntSlider classes which do not raise exceptions when instantiated. This allows the patched @interact to handle the missing ipywidgets scenario gracefully.

After applying the changes suggested in this PR the ImportError is raised as intended.

$ python -c "import seaborn; seaborn.choose_colorbrewer_palette('quatlitative')"

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "<redacted>/seaborn/seaborn/widgets.py", line 141, in choose_colorbrewer_palette
    @interact
     ^^^^^^^^
  File "<redacted>/seaborn/seaborn/widgets.py", line 10, in interact
    raise ImportError(msg)
ImportError: Interactive palettes require `ipywidgets`, which is not installed.