refactor(box libfuncs): use BlockExt trait

[FeliGR]

Checklist

• [ lambdaclass/cairo_native/issues/521 ] Linked to Github Issue
• [ ] Unit tests added
• [ ] Integration tests added.
• [ ] This change requires new documentation.
  • [ ] Documentation has been added/updated.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 92.30769% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 88.69%. Comparing base (1bbda33) to head (b782a6c). Report is 8 commits behind head on main.

Files	Patch %	Lines
src/libfuncs/box.rs	92.30%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #545      +/-   ##
==========================================
- Coverage   88.85%   88.69%   -0.17%     
==========================================
  Files         108      108              
  Lines       34555    34242     -313     
==========================================
- Hits        30705    30372     -333     
- Misses       3850     3870      +20     

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[juanbono]

Please fix conflict @FeliGR