feat(layout): allow more serialization with serde

[EdJoPaTo]

similar to Rect

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.

Project coverage is 94.5%. Comparing base (b344f95) to head (ac67df9).

Files	Patch %	Lines
src/layout/margin.rs	0.0%	1 Missing ⚠️
src/layout/position.rs	0.0%	1 Missing ⚠️
src/layout/rect.rs	0.0%	1 Missing ⚠️
src/layout/size.rs	0.0%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #1255     +/-   ##
=======================================
- Coverage   94.6%   94.5%   -0.1%     
=======================================
  Files         65      65             
  Lines      15407   15411      +4     
=======================================
  Hits       14576   14576             
- Misses       831     835      +4     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.