Apply device inactivity threshold at initial import time

[Andrew-Dickinson]

Apply the same thresholding logic to abandon date for devices at initial import time as we do on continuous UISP imports, to prevent devices being prematurely marked inactive

Also add missing newline to -------- separator

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.18%. Comparing base (7b21c21) to head (9774499).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #632   +/-   ##
=======================================
  Coverage   94.18%   94.18%           
=======================================
  Files          79       79           
  Lines        3235     3235           
=======================================
  Hits         3047     3047           
  Misses        188      188           

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