fix: no animation on first lut expansion

[tlambert03]

Don't animate lut expansion on initial widget show.

There is also a bug in superqt that will need to be fixed for this to work: pyapp-kit/superqt#331

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.01%. Comparing base (24cb779) to head (8bf7d1b).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #232      +/-   ##
==========================================
- Coverage   86.03%   86.01%   -0.02%     
==========================================
  Files          46       46              
  Lines        5228     5228              
==========================================
- Hits         4498     4497       -1     
- Misses        730      731       +1     

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