feat(mve): add support for gwe-gwe exchanges that include mve package

[emorway-usgs]

model-level MVE package was previously supported by virtue of the dfn file. However, simulation-level support for MVE was not supported. A new autotest for MF6 confirms that these changes are sufficient.

This missing functionality was discovered when attempting to support parallel energy mover (MVE) transport in MF6. For example, if a stream was split across two flow and transport models and a transport mover was required to properly route solute from an SFT reach in one model to a connected SFT reach in a downstream model, MVT worked, but its complement in GWE, namely MVE, was not working prior to this PR.

[codecov]

Codecov Report

❌ Patch coverage is 60.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.4%. Comparing base (556c088) to head (a692612).
⚠️ Report is 153 commits behind head on develop.

Files with missing lines	Patch %	Lines
flopy/mf6/utils/codegen/filters.py	0.0%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2750      +/-   ##
===========================================
+ Coverage     55.5%    72.4%   +16.8%     
===========================================
  Files          644      675      +31     
  Lines       124135   132046    +7911     
===========================================
+ Hits         68947    95632   +26685     
+ Misses       55188    36414   -18774     

Files with missing lines	Coverage Δ
flopy/mf6/data/mfstructure.py	74.1% <100.0%> (+0.4%)	⬆️
flopy/mf6/utils/codegen/component.py	0.0% <ø> (ø)
flopy/mf6/utils/codegen/filters.py	0.0% <0.0%> (ø)

... and 572 files with indirect coverage changes

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[wpbonelli]

Looks good to me. I know it's not ideal to have to do this manually but it's temporary. In 4.x mfstructure.py will go away, and we can hopefully drop the special casing in the new code generation logic too.