Refactor ItemMetadata to NKFile conversion as NKFile extension method

[claucambra]

Simplifies this a lot

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 92.10526% with 6 lines in your changes missing coverage. Please review.

Project coverage is 76.55%. Comparing base (6bc6961) to head (61e7b3d).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
...FileProviderKit/Extensions/NKFile+Extensions.swift	93.05%	5 Missing ⚠️
...roviderKit/Enumeration/Enumerator+SyncEngine.swift	50.00%	1 Missing ⚠️

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Additional details and impacted files

@@           Coverage Diff           @@
##             main      #26   +/-   ##
=======================================
  Coverage   76.55%   76.55%           
=======================================
  Files          38       39    +1     
  Lines        8174     8174           
=======================================
  Hits         6258     6258           
  Misses       1916     1916           

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