update(ModflowWel): add basic support for mfnwt tabfile based well files

[jlarsen-usgs]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.5%. Comparing base (556c088) to head (42e7ec3).
⚠️ Report is 163 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2755      +/-   ##
===========================================
+ Coverage     55.5%    72.5%   +17.0%     
===========================================
  Files          644      677      +33     
  Lines       124135   132656    +8521     
===========================================
+ Hits         68947    96260   +27313     
+ Misses       55188    36396   -18792     

Files with missing lines	Coverage Δ
flopy/modflow/mfwel.py	88.1% <100.0%> (-1.9%)	⬇️
flopy/pakbase.py	82.8% <100.0%> (-1.7%)	⬇️

... and 578 files with indirect coverage changes

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[jlarsen-usgs]

Testing failure should be fixed with #2757