fix: only notify ui of selection change if it actually changed

[Xazin]

Just a minor thing I noticed, if I have an empty node and I'm dragging horizontally, I could see the cursor blinking fast as if the selection updates all the time, but we shouldn't notify about the update unless the selection actually did change.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 71.94%. Comparing base (98356fa) to head (620322f).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
...t/service/selection/desktop_selection_service.dart	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #914      +/-   ##
==========================================
- Coverage   71.94%   71.94%   -0.01%     
==========================================
  Files         318      318              
  Lines       14980    14981       +1     
==========================================
  Hits        10778    10778              
- Misses       4202     4203       +1     

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