feat: add range slider (take 2)

[tlambert03]

a slightly more minimal take on adding range slider. This doesn't worry about using superqt's labeled sliders, just implements a range slider.

cc @brisvag, I added you as a co-author

closes #337

[codecov[bot]]

Codecov Report

Merging #455 (8de3204) into main (f34bb42) will increase coverage by 0.05%. The diff coverage is 94.44%.

:exclamation: Current head 8de3204 differs from pull request most recent head 80110b2. Consider uploading reports for the commit 80110b2 to get more accurate results

@@            Coverage Diff             @@
##             main     #455      +/-   ##
==========================================
+ Coverage   87.77%   87.82%   +0.05%     
==========================================
  Files          31       31              
  Lines        4113     4156      +43     
==========================================
+ Hits         3610     3650      +40     
- Misses        503      506       +3     

Impacted Files	Coverage Δ
magicgui/backends/_qtpy/__init__.py	100.00% <ø> (ø)
magicgui/widgets/__init__.py	100.00% <ø> (ø)
magicgui/backends/_qtpy/widgets.py	87.01% <90.62%> (+0.06%)	:arrow_up:
magicgui/widgets/_bases/__init__.py	100.00% <100.00%> (ø)
magicgui/widgets/_bases/ranged_widget.py	88.88% <100.00%> (+0.95%)	:arrow_up:
magicgui/widgets/_bases/slider_widget.py	96.66% <100.00%> (+0.23%)	:arrow_up:
magicgui/widgets/_concrete.py	86.83% <100.00%> (+0.10%)	:arrow_up:

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[tlambert03]

looks like the tests here will need superqt v0.3.6 ... which is in prerelease now. will update in a week or so

[brisvag]

Awesome! So the issue we were having with signals emitting/receeving the wrong types is solved?