add RadioButtons widget

[tlambert03]

This adds widgets.RadioButtons which has the same API as widgets.ComboBox (with the addition of an orientation parameter). Currently, only exclusive radio groups are supported.

shown here with horizontal orientation in a vertical layout:

[codecov]

Codecov Report

Merging #183 (ecef170) into master (16cda7c) will increase coverage by 0.01%.
The diff coverage is 83.75%.

@@            Coverage Diff             @@
##           master     #183      +/-   ##
==========================================
+ Coverage   90.06%   90.07%   +0.01%     
==========================================
  Files          29       29              
  Lines        2908     2982      +74     
==========================================
+ Hits         2619     2686      +67     
- Misses        289      296       +7     

Impacted Files	Coverage Δ
magicgui/backends/_qtpy/__init__.py	100.00% <ø> (ø)
magicgui/widgets/__init__.py	100.00% <ø> (ø)
magicgui/widgets/_protocols.py	99.44% <ø> (-0.01%)	⬇️
magicgui/backends/_qtpy/widgets.py	86.90% <81.15%> (-0.06%)	⬇️
magicgui/widgets/_bases/categorical_widget.py	83.87% <100.00%> (+3.22%)	⬆️
magicgui/widgets/_concrete.py	84.59% <100.00%> (+0.36%)	⬆️

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[sofroniewn]

Looks good to me! By default will you get the opposite orientation of the orientation of the main layout if possible? So always some combo of vertical + horizontal. Or is that maybe too magical? You could always fallback on a single default if nothing else makes sense

[tlambert03]

By default will you get the opposite orientation of the orientation of the main layout if possible?

I was just gonna stick with vertical by default... someone won't like the magic :)

[sofroniewn]

I was just gonna stick with vertical by default... someone won't like the magic :)

fine with me!

[jni]

❤️