Fix bug in creation of RangeEdit using create_widget

[Czaki]

When run this code

from magicgui.widgets import create_widget

w = create_widget(annotation=range)

it ends with error:

Traceback (most recent call last):
  File "/home/czaki/Projekty/neutrofile/Tutorial/sample_magicgui.py", line 3, in <module>
    w = create_widget(annotation=range)
  File "/home/czaki/.pyenv/versions/3.8.3/envs/neutrofile/lib/python3.8/site-packages/magicgui/widgets/_bases/create_widget.py", line 96, in create_widget
    widget = wdg_class(**kwargs)
  File "/home/czaki/.pyenv/versions/3.8.3/envs/neutrofile/lib/python3.8/site-packages/magicgui/widgets/_concrete.py", line 558, in __init__
    raise TypeError(f"Invalid value type for {type(self)}: {type(value)}")
TypeError: Invalid value type for <class 'magicgui.widgets.RangeEdit'>: <class 'magicgui.widgets._bases.value_widget._Unset'>

When fixing this error by checking if value is None or UNSET then also happens problem with an unexpected nullable field.
The second error I fix by pop the nullable from kwargs. But I'm not sure if it is the correct solution.

[codecov]

Codecov Report

Merging #396 (db95b7d) into main (56e419d) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #396      +/-   ##
==========================================
- Coverage   88.61%   88.59%   -0.03%     
==========================================
  Files          30       30              
  Lines        3796     3797       +1     
==========================================
  Hits         3364     3364              
- Misses        432      433       +1     

Impacted Files	Coverage Δ
magicgui/widgets/_concrete.py	85.42% <100.00%> (+0.02%)	⬆️
magicgui/_type_wrapper.py	67.87% <0.00%> (-0.37%)	⬇️

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[tlambert03]

thanks @Czaki! These changes make sense / work for me. more broadly, I think the issue here stems from having these "container-based" classes that more or less implement the ValueWidget protocol, but don't directly inherit from valuewidget. (see https://github.com/napari/magicgui/issues/372).

This change is totally fine with me as a first step... maybe in the future, I can get around to making them actually be ValueWidgets (in which case nullable should work again, and allow things like create_widget(annotation=Optional[range])

[Czaki]

ValueWidget

it will be also nice if create_widget return ValueWidget, not Widget (type annotation, documentation etc)

[tlambert03]

This came up before in some issue, can't find it atm, since not all widgets are necessarily value widgets, I'm not sure that's the proper annotation?

[Czaki]

Hm. In general I know because Container is also widget. But what input to create_widget could create non-value widget?

Or you think about user registered widget?

[tlambert03]

But what input to create_widget could create non-value widget?

Yeah, thats a good question :)

I can't immediately think of one. I'm open to it. I remember trying to change it one point and then realizing that changing that annotation requires a lot of other type changes elsewhere, but it might be worth it. Feel free to dig a bit deeper if you're interested

[Czaki]

If I should fix somehow failing test? It looks non-related.