small refactor in artifacts.nx_gx()

[jGaboardi]

This PR is a small DRY/refactor in artifacts.nx_gx().

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.8%. Comparing base (fd6e747) to head (031b5d5).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #154     +/-   ##
=======================================
- Coverage   98.8%   98.8%   -0.0%     
=======================================
  Files          6       6             
  Lines       1000     998      -2     
=======================================
- Hits         988     986      -2     
  Misses        12      12             

Files with missing lines	Coverage Δ
neatnet/artifacts.py	97.9% <100.0%> (-<0.1%)	⬇️