fix (flatten): flattening transforms was losing curves

[lallmon]

No description provided.

[codecov]

Codecov Report

❌ Patch coverage is 94.20290% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.17%. Comparing base (897b26c) to head (1058baf).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/lucent/canvas_model.py	92.85%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #167      +/-   ##
==========================================
+ Coverage   92.14%   92.17%   +0.03%     
==========================================
  Files          23       23              
  Lines        3576     3643      +67     
==========================================
+ Hits         3295     3358      +63     
- Misses        281      285       +4     

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