Calculate nlinks

[twiggler]

Closes #8

[codecov]

Codecov Report

Attention: Patch coverage is 94.73684% with 1 line in your changes missing coverage. Please review.

Project coverage is 88.56%. Comparing base (a37a8d2) to head (edd2a02).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
dissect/jffs/jffs2.py	94.73%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #13      +/-   ##
==========================================
+ Coverage   88.09%   88.56%   +0.46%     
==========================================
  Files           4        4              
  Lines         252      271      +19     
==========================================
+ Hits          222      240      +18     
- Misses         30       31       +1     

Flag	Coverage Δ
unittests	88.56% <94.73%> (+0.46%)	⬆️

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[Schamper]

Just a note that this code will massively benefit from fox-it/dissect.cstruct#114