feat(grb): add binary grid file reader, support grid file in fmi (WIP)

[wpbonelli]

Introduce a GridFileReader module with ability to load variables from a binary grid file. Use this from fmi packages, if a new GWFGRID entry is provided in fmi package data, to facilitate an identical check to that introduced in #2149 for exchanges.

This module generalizes the approach in grb.f90 and replaces that module. The converter can use the new module.

The tentative idea is to make the grid file optional for fmi for some time, then begin to require it, in the interest of catching user errors. At which point the GridFileReader could be modified to load the entire discretization, and we can do a robust grid comparison as discussed in #2149. For now, the reader loads headers and builds an index of the file at init time, after which variables can be read as necessary.

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Checklist of items for pull request

• Replaced section above with description of pull request
• Added new test or modified an existing test
• Formatted new and modified Fortran source files with fprettify
• Added doxygen comments to new and modified procedures
• Updated meson files, makefiles, and Visual Studio project files for new source files
• Updated definition files
• Updated develop.tex with a plain-language description of the bug fix, change, feature; required for changes that may affect users
• Updated input and output guide
• Removed checklist items not relevant to this pull request