utils: move memdup from libsqsh to cextras

[Gottox]

This change moves the sqsh_memdup() function from libsqsh to cextras.

[codecov]

Codecov Report

Patch coverage: 50.00% and project coverage change: -0.02% ⚠️

Comparison is base (60a6b67) 59.21% compared to head (5d844d2) 59.19%.
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #115      +/-   ##
==========================================
- Coverage   59.21%   59.19%   -0.02%     
==========================================
  Files          58       58              
  Lines        4742     4735       -7     
  Branches      710      708       -2     
==========================================
- Hits         2808     2803       -5     
  Misses       1524     1524              
+ Partials      410      408       -2     

Files Changed	Coverage Δ
lib/directory/directory_iterator.c	75.98% <ø> (-0.88%)	⬇️
lib/file/file.c	59.77% <0.00%> (ø)
lib/utils/utils.h	100.00% <ø> (+23.52%)	⬆️
lib/xattr/xattr_iterator.c	70.19% <100.00%> (ø)

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