Fix 2583

[wpbonelli]

• reproduce bug: External file write fails when passing cellid as [k,i,j] list in stress period data #2583
• restore support for list form of cell ID
• update test to check list data written to file

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.5%. Comparing base (556c088) to head (8b92fd4).
⚠️ Report is 36 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2584      +/-   ##
===========================================
+ Coverage     55.5%    72.5%   +16.9%     
===========================================
  Files          644      667      +23     
  Lines       124135   128601    +4466     
===========================================
+ Hits         68947    93251   +24304     
+ Misses       55188    35350   -19838     

Files with missing lines	Coverage Δ
flopy/mf6/data/mfdataplist.py	72.9% <100.0%> (-6.0%)	⬇️

... and 405 files with indirect coverage changes

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