Add birthtime_ns to ExtFilesystemEntry.lstat

[Miauwkeru]

closes #875

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.44%. Comparing base (7e856fd) to head (e84b689).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #876      +/-   ##
==========================================
+ Coverage   76.40%   76.44%   +0.03%     
==========================================
  Files         314      314              
  Lines       26927    26928       +1     
==========================================
+ Hits        20574    20585      +11     
+ Misses       6353     6343      -10     

Flag	Coverage Δ
unittests	76.44% <100.00%> (+0.03%)	⬆️

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