Remove internal event connection on SelectableEventedList

[andy-sweet]

Description

We try to avoid internal event connections, likely to avoid circular references. This PR removes such an internal event connection and also closes that particular TODO/FIXME.

It also adds tests to ensure we still get the desired behavior of removing a deleted item from the current selection.

Type of change

• Bug-fix (non-breaking change which fixes an issue)

References

An alternative to #4534

How has this been tested?

• added new tests to cover expected behavior
• all existing tests pass with my change

[alisterburt]

Looks great! Thanks for taking over. For info I think there were/are two reasons for not liking the code as it was, internal event connection and connection to a lambda. As I understand it internal event connection is just a bit harder to reason about and connecting to lambdas is a potential cause of the cleanup bugs we see in Qt tests sometimes

[andy-sweet]

Looks like there's a real failure related to LayerList. Will look into it later today.

[codecov]

Codecov Report

Merging #5339 (1039d89) into main (c969968) will decrease coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #5339      +/-   ##
==========================================
- Coverage   89.10%   89.06%   -0.04%     
==========================================
  Files         582      583       +1     
  Lines       49313    49336      +23     
==========================================
+ Hits        43938    43939       +1     
- Misses       5375     5397      +22     

Impacted Files	Coverage Δ
napari/components/_tests/test_layers_list.py	100.00% <ø> (ø)
napari/components/layerlist.py	92.51% <100.00%> (+0.05%)	⬆️
napari/utils/events/_tests/test_selectable_list.py	100.00% <100.00%> (ø)
napari/utils/events/containers/_evented_list.py	95.90% <100.00%> (ø)
napari/utils/events/containers/_selectable_list.py	80.00% <100.00%> (+0.33%)	⬆️
napari/_tests/test_draw.py	36.84% <0.00%> (-63.16%)	⬇️
napari/layers/tracks/_track_utils.py	87.50% <0.00%> (-3.41%)	⬇️
napari/_qt/widgets/qt_color_swatch.py	71.54% <0.00%> (-3.26%)	⬇️
napari/utils/interactions.py	74.52% <0.00%> (-2.84%)	⬇️
napari/utils/info.py	80.00% <0.00%> (-2.23%)	⬇️
... and 6 more

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[andy-sweet]

Looks like there's a real failure related to LayerList. Will look into it later today.

Fixed. Needed to call the super implementation of the deletion handler in LayerList's implementation.