Refactored nullable libfuncs to use the BlockExt trait

[tcoratger]

Checklist

• 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 75.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 91.87%. Comparing base (b2f1568) to head (c05c63e).
Report is 8 commits behind head on main.

Files	Patch %	Lines
src/libfuncs/nullable.rs	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #660      +/-   ##
==========================================
- Coverage   91.95%   91.87%   -0.09%     
==========================================
  Files         112      113       +1     
  Lines       34265    34581     +316     
==========================================
+ Hits        31509    31771     +262     
- Misses       2756     2810      +54     

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