fix(modflow): dataframe support was patchy in a few packages

[wpbonelli]

• motivated by Example of using Pandas to specify stress period data #2135
• followup to feat(modflow): support dataframe for pkg data #2010
• patch a few remaining gaps in support for dataframes
• update mf6_mnw2_tutorial01.py to use dataframe pkg input
• update a test in test_modflow.py to use dataframe pkg input

[codecov]

Codecov Report

Attention: Patch coverage is 87.50000% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 73.0%. Comparing base (4c44cb0) to head (54bdf7b).

Additional details and impacted files

@@            Coverage Diff            @@
##           develop   #2136     +/-   ##
=========================================
+ Coverage     71.1%   73.0%   +1.9%     
=========================================
  Files          260     260             
  Lines        58076   59483   +1407     
=========================================
+ Hits         41341   43482   +2141     
+ Misses       16735   16001    -734     

Files	Coverage Δ
flopy/modflow/mfmnw2.py	83.1% <100.0%> (+<0.1%)	⬆️
flopy/utils/util_list.py	74.7% <100.0%> (ø)
flopy/modflow/mfriv.py	92.1% <83.3%> (-0.9%)	⬇️

... and 108 files with indirect coverage changes