refactor(datafile): ignore "text" parameter, add attributes from file

[mwtoews]

This PR ignores the text= parameter from HeadFile, HeadUFile and UcnFile, since this should be read from the file and is constant for all records. This PR adds these attributes:

• obj.text_bytes, the 16-byte char bytes obtained from the file
• obj.text, a str version of this field, .e.g., used by flopy.export for NetCDF variable names

There are instances where other binary files can be attempted to be read (e.g. "mt3d_test/mf96mt3d/P01/case1b/MT3D001.UCN" with HeadFile), but these are now caught with exceptions raised. Warnings are raised if the text records are inconsistent, which shouldn't happen (unless I've misunderstood something!)

[mwtoews]

This does have a breaking change, where previously the obj.text attribute was bytes, and now changed to str. For instance:

Before:

>>> pth = example_data_path / "unstructured/headu.githds"
>>> obj = flopy.utils.binaryfile.HeadUFile(pth)
>>> obj.text
b'headu'

After:

>>> obj = flopy.utils.binaryfile.HeadUFile(pth)
>>> obj.text
'headu'
>>> obj.text_bytes
b'           HEADU'

if this is a deal-breaker, then obj.text can be kept as the modified bytes (possibly raising a deprecation message if accessed), and the str version of the attribute instead stored at obj.text_str.

Also, I should note that this PR does not change FormattedHeadFile, since further refactoring may be needed.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 63.15789% with 7 lines in your changes missing coverage. Please review.

Project coverage is 70.8%. Comparing base (e2a85a3) to head (fb14357).

Additional details and impacted files

@@            Coverage Diff            @@
##           develop   #2231     +/-   ##
=========================================
- Coverage     70.8%   70.8%   -0.1%     
=========================================
  Files          294     294             
  Lines        59026   59029      +3     
=========================================
- Hits         41832   41804     -28     
- Misses       17194   17225     +31     

Files	Coverage Δ
flopy/export/vtk.py	78.0% <100.0%> (-0.1%)	:arrow_down:
flopy/utils/binaryfile.py	81.7% <100.0%> (+0.1%)	:arrow_up:
flopy/utils/datafile.py	73.6% <100.0%> (+0.3%)	:arrow_up:
flopy/mf6/utils/binaryfile_utils.py	10.6% <0.0%> (ø)
flopy/export/utils.py	59.0% <16.6%> (-2.4%)	:arrow_down:

... and 6 files with indirect coverage changes

[mwtoews]

Thanks @langevin-usgs for the info, I'll create and add a mixed text example to test, e.g. head/drawdown. The text parameter can be changed to optional, which would default to read the first text header, and warn if more than one found.

[mwtoews]

Confirmed I can create the mixed-text file with older MF versions, and testing current and ancient versions of flopy I can see this feature has never worked. I'll superseded this PR with a fix after a few other related refactors that use the .headers data frame property.