refactor(datafile): deprecate list_records() and other list_ methods

[mwtoews]

Now that data files have a .headers data frame property (#2221), there is no need to have methods that print parts of this information to stdout (they return None). This PR deprecates the following:

• list_records(): use headers instead
• list_unique_records(): use headers[["text", "imeth"]].drop_duplicates() instead
• list_unique_packages(to=True/False): use headers.paknam.drop_duplicates() or headers.paknam2.unique() (there are a few ways)

The last two only apply to CellBudgetFile. This PR does not apply to flopy.mf6.utils.mfobservation.list_records().

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.8%. Comparing base (e2a85a3) to head (d331ae1).
Report is 1 commits behind head on develop.

Additional details and impacted files

@@            Coverage Diff            @@
##           develop   #2232     +/-   ##
=========================================
- Coverage     70.8%   70.8%   -0.1%     
=========================================
  Files          294     294             
  Lines        59026   59025      -1     
=========================================
- Hits         41832   41806     -26     
- Misses       17194   17219     +25     

Files	Coverage Δ
flopy/utils/binaryfile.py	82.0% <100.0%> (+0.5%)	⬆️
flopy/utils/datafile.py	74.7% <100.0%> (+1.4%)	⬆️
flopy/utils/formattedfile.py	88.9% <ø> (ø)

... and 9 files with indirect coverage changes