Fix open/close bugs

[hansonmcoombs]

Fix 2 bugs regarding MFList when reading external files.

First, allow the use of pathlib.Path objects rather than just strings

Second, fix a bug where calculating mxact raises an error when reading a stress period file with only one feature.

Created two new tests to support these features and ran all automated tests. The only failures were:

• autotest.test_mbase.test_resolve_exe_by_abs_path
• autotest.test_mbase.test_resolve_exe_by_name
• autotest.test_example_notebooks.test_notebooks
• autotest.regression.test_mf6.test006_2models_different_dis
• autotest.regression.test_mf6.test006_create_tests_2models_gnc

From the traceback I belive that these failures are based on my configuration and setup not the changes (note that many of these are not related to Modflow2005/nwt

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.6%. Comparing base (556c088) to head (09b61fb).
⚠️ Report is 79 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2638      +/-   ##
===========================================
+ Coverage     55.5%    72.6%   +17.0%     
===========================================
  Files          644      667      +23     
  Lines       124135   129132    +4997     
===========================================
+ Hits         68947    93770   +24823     
+ Misses       55188    35362   -19826     

Files with missing lines	Coverage Δ
flopy/utils/util_list.py	73.6% <100.0%> (-2.1%)	⬇️

... and 559 files with indirect coverage changes

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[mwtoews]

Howdy Matt, I've provided a few suggestions.

[hansonmcoombs]

@mwtoews sorted