fix(exchange and gnc package cellids): #1866

[spaulins-usgs]

Fixed exchange and gnc package cellids to resolve model number properly, for simulations with multiple models (#1841)

[codecov]

Codecov Report

Merging #1871 (a345070) into develop (a16a379) will increase coverage by 2.2%.
The diff coverage is 77.2%.

@@            Coverage Diff            @@
##           develop   #1871     +/-   ##
=========================================
+ Coverage     69.9%   72.2%   +2.2%     
=========================================
  Files          257     257             
  Lines        56206   56226     +20     
=========================================
+ Hits         39323   40621   +1298     
+ Misses       16883   15605   -1278     

Impacted Files	Coverage Δ
flopy/mf6/data/mfdatautil.py	53.8% <54.5%> (+1.6%)	⬆️
flopy/mf6/data/mfdatascalar.py	60.7% <55.5%> (+1.7%)	⬆️
flopy/mf6/coordinates/modeldimensions.py	79.0% <60.0%> (+5.7%)	⬆️
flopy/mf6/utils/testutils.py	9.9% <66.6%> (-0.1%)	⬇️
flopy/utils/datautil.py	63.9% <92.3%> (+0.7%)	⬆️
flopy/mf6/data/mfdatalist.py	72.3% <100.0%> (+1.8%)	⬆️
flopy/mf6/data/mfdatastorage.py	71.2% <100.0%> (+3.2%)	⬆️
flopy/mf6/data/mffileaccess.py	71.7% <100.0%> (+0.7%)	⬆️
flopy/mf6/mfsimbase.py	65.3% <100.0%> (+5.4%)	⬆️

... and 54 files with indirect coverage changes