Copy nodes from source

[AnniekStok]

Support copying of points or labels from a source layer as new nodes.

The execution of the copy depends on the click location (background, same track, different track), whether preserve labels is active, and whether the option 'copy as new track' is active (in case a node with current track ID already exists a current time point).

For now this behavior is linked to right-mouse clicks, but that is up for discussion. I also added a keybind for starting a new track ('), and disabled centering to the selected node when undoing/redoing (also up for discussion, I just found it rather annoying that it would jump to a different z position when I wanted to undo something).

Needs a small update on Funtracks to allow _top_level=True/False on UserUpdateSegmentation and UserDeleteNodes, because replacing a label with a copied smaller other label consists of multiple actions (erase and paint), that we would want to undo as a single Action in one go (funkelab/funtracks#271)

[codecov-commenter]

Codecov Report

❌ Patch coverage is 79.51807% with 102 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.18%. Comparing base (9546021) to head (3b0a081).

Files with missing lines	Patch %	Lines
...motile_tracker/application_menus/layer_dropdown.py	55.73%	54 Missing ⚠️
...acker/application_menus/copy_from_source_widget.py	87.75%	42 Missing ⚠️
src/motile_tracker/data_views/views/ortho_views.py	50.00%	4 Missing ⚠️
...le_tracker/data_views/views/layers/track_points.py	0.00%	1 Missing ⚠️
...cker/data_views/views_coordinator/tracks_viewer.py	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #477      +/-   ##
==========================================
- Coverage   88.81%   88.18%   -0.64%     
==========================================
  Files          59       61       +2     
  Lines        5776     6261     +485     
==========================================
+ Hits         5130     5521     +391     
- Misses        646      740      +94     

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[cmalinmayor]

Can we simplify this to just one segmentation channel? And then open another issue to talk about our general approach to axis validation and having things in the viewer that aren't only t [z] y x? I think that's a bigger issue, since right now we (implicitly) assume that the viewer.dims are the same as the tracks dims, and we probably should relax that, but more rigorously.

[AnniekStok]

I agree we should split it. Can we fix the dims issue first? I think the copy from source feature has much less practical value if the multichannel option is not there.