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

[wpbonelli]

• motivated by #2135
• followup to #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[bot]]

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

```diff @@ 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](https://app.codecov.io/gh/modflowpy/flopy/pull/2136?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=modflowpy) | Coverage Δ | | |---|---|---| | [flopy/modflow/mfmnw2.py](https://app.codecov.io/gh/modflowpy/flopy/pull/2136?src=pr&el=tree&filepath=flopy%2Fmodflow%2Fmfmnw2.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=modflowpy#diff-ZmxvcHkvbW9kZmxvdy9tZm1udzIucHk=) | `83.1% <100.0%> (+<0.1%)` | :arrow_up: | | [flopy/utils/util\_list.py](https://app.codecov.io/gh/modflowpy/flopy/pull/2136?src=pr&el=tree&filepath=flopy%2Futils%2Futil_list.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=modflowpy#diff-ZmxvcHkvdXRpbHMvdXRpbF9saXN0LnB5) | `74.7% <100.0%> (ø)` | | | [flopy/modflow/mfriv.py](https://app.codecov.io/gh/modflowpy/flopy/pull/2136?src=pr&el=tree&filepath=flopy%2Fmodflow%2Fmfriv.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=modflowpy#diff-ZmxvcHkvbW9kZmxvdy9tZnJpdi5weQ==) | `92.1% <83.3%> (-0.9%)` | :arrow_down: | ... and [108 files with indirect coverage changes](https://app.codecov.io/gh/modflowpy/flopy/pull/2136/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=modflowpy)