mfgrdfile: add version and crs properties

[mjreno]

Add GRB v2 binary grid file support (CRS, version, export)

• Adds version and crs properties to MfGrdFile for reading GRB v1 and v2 files
• Extends MfGrdFile.export() to write GRB v2 files with embedded CRS; auto-detects output version based on CRS presence; supports int, str, and pyproj.CRS inputs via _crs_to_string()

Fixed issues:

1. Header newline placement: write_line() was not placing \n at the fixed position 49; Fortran readers parse header and definition lines as fixed-length text records and require the newline exactly at the end position
2. Array write order: arrays were flattened with order="F" (column-major); multi-dimensional arrays in _datadict (e.g. DISV BOTM, reshaped to (nlay, ncpl)) were written cell-major instead of layer-major; fixed to order="C" to match MF6 on-disk layout
3. Variable list hardcoded shapes: develop's export() hardcoded per-grid-type variable lists with manually specified shapes; replaced with shapes derived from _recorddict (parsed source file structure), fixing incorrect DIS TOP array shape

[codecov]

Codecov Report

❌ Patch coverage is 84.28571% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.5%. Comparing base (556c088) to head (01f785f).
⚠️ Report is 179 commits behind head on develop.

Files with missing lines	Patch %	Lines
flopy/mf6/utils/binarygrid_util.py	84.2%	11 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2711      +/-   ##
===========================================
+ Coverage     55.5%    72.5%   +17.0%     
===========================================
  Files          644      677      +33     
  Lines       124135   132721    +8586     
===========================================
+ Hits         68947    96354   +27407     
+ Misses       55188    36367   -18821     

Files with missing lines	Coverage Δ
flopy/mf6/utils/binarygrid_util.py	89.5% <84.2%> (-1.3%)	⬇️

... and 579 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.