fix(datafile): fix mixed-text file behavior

[wpbonelli]

This PR builds on #2231.

Ignoring text breaks the only mechanism to access secondary record types in a mixed-text file (e.g. DRAWDOWN in a HEAD+DRAWDOWN file).

Keep text functional. The new headers can contain all of the headers in the file, regardless of record type, while recordarray holds only records of type text.

Keep doing substring matching when filtering by text.

Make BinaryLayerFile public. Default text=None and automatically read it from the first header in the file. Warn on mixed-text files i.e. more than one record type.

Add a unique_records property which will in most cases have a single element, multiple for mixed-text files.

I think it's cleanest for these file handle classes to scope to a single record type like this. With the addition of headers and unique_records one can easily see if a file is mixed-text, then open separate handles for the other record types.

BinaryLayerFile becomes the recommended entry point for MF6 advanced package output files (LAK, SFR, UZF, etc.) where the text label isn't known in advance, so we avoid the HeadFile naming mismatch.

Child class defaults stay the same: HeadFile(text="head"), UcnFile(text="concentration"), HeadUFile(text="headu"). Raise if no records matching the given text are found. So HeadFile("model.ddn") will error. But HeadFile("model.ddn", text="drawdown") or BinaryLayerFile("model.ddn") will work.

[codecov]

Codecov Report

❌ Patch coverage is 75.64103% with 19 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.4%. Comparing base (556c088) to head (0844df4).
⚠️ Report is 131 commits behind head on develop.

Files with missing lines	Patch %	Lines
flopy/utils/binaryfile/__init__.py	84.3%	10 Missing ⚠️
flopy/export/utils.py	16.6%	5 Missing ⚠️
flopy/mf6/utils/binaryfile_utils.py	0.0%	2 Missing ⚠️
flopy/export/vtk.py	0.0%	1 Missing ⚠️
flopy/utils/datafile.py	75.0%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2714      +/-   ##
===========================================
+ Coverage     55.5%    72.4%   +16.8%     
===========================================
  Files          644      674      +30     
  Lines       124135   130634    +6499     
===========================================
+ Hits         68947    94585   +25638     
+ Misses       55188    36049   -19139     

Files with missing lines	Coverage Δ
flopy/utils/__init__.py	100.0% <100.0%> (ø)
flopy/export/vtk.py	68.4% <0.0%> (-9.7%)	⬇️
flopy/utils/datafile.py	71.6% <75.0%> (-2.7%)	⬇️
flopy/mf6/utils/binaryfile_utils.py	10.6% <0.0%> (-42.1%)	⬇️
flopy/export/utils.py	53.6% <16.6%> (-11.0%)	⬇️
flopy/utils/binaryfile/__init__.py	82.2% <84.3%> (-2.3%)	⬇️

... and 566 files with indirect coverage changes

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