feat(cellbudgetfile): support aux vars with full3D in get_data()

[wpbonelli]

Add a variable parameter (default "q") to get_data() and get_record() to allow specifying the field to extract to a 3D grid-shaped array. Previously "q" was returned unconditionally.

variable is only supported when full3D=True and the method's default behavior is unchanged.

sat = cbc.get_data(text="DATA-SAT", full3D=True, variable="sat")[0]

This is consistent with the existing variable parameter in get_ts(), added in #2568

Close #2774.

[codecov]

Codecov Report

❌ Patch coverage is 92.30769% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 72.5%. Comparing base (556c088) to head (e5414d1).
⚠️ Report is 177 commits behind head on develop.

Files with missing lines	Patch %	Lines
flopy/utils/binaryfile/__init__.py	92.3%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2776      +/-   ##
===========================================
+ Coverage     55.5%    72.5%   +17.0%     
===========================================
  Files          644      677      +33     
  Lines       124135   132649    +8514     
===========================================
+ Hits         68947    96287   +27340     
+ Misses       55188    36362   -18826     

Files with missing lines	Coverage Δ
flopy/utils/binaryfile/__init__.py	74.6% <92.3%> (-9.9%)	⬇️

... and 579 files with indirect coverage changes

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