refactor(padding): zero as a constant

[EdJoPaTo]

A const fn with no input is probably a constant.

-Padding::zero()
+Padding::ZERO

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 94.2%. Comparing base (cf67ed9) to head (0a8ee15).

Files	Patch %	Lines
src/widgets/block/padding.rs	0.0%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #1133     +/-   ##
=======================================
- Coverage   94.2%   94.2%   -0.1%     
=======================================
  Files         60      60             
  Lines      14630   14623      -7     
=======================================
- Hits       13790   13780     -10     
- Misses       840     843      +3     

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