Unified wrf/wrf-chem model_mod

[hkershaw-brown]

Description:

Refactored WRF model mod for WRF & WRF CHEM.
Namelist selectable QTYS, see #404 for details.

Created a wrf_unified model directory. This is to allow concurrent development on wrf and wrf_unified.
wrf_unified/model_mod is ~4500 less than the wrf/model_mod and this is a bit of a headache for keeping up-to-date with main (easy to miss changes in such differing code).

See pull #683 for original pull request
wrf-wrf-chem branch available at https://github.com/hkershaw-brown/DART/tree/wrf-wrf-chem

Fixes issue

Fixes #404
Partial #359 (WRF)
Partial #624 (WRF)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

Documentation changes needed?

• My change requires a change to the documentation.
  • I have updated the documentation accordingly.

Tests

Please describe any tests you ran to verify your changes.
Bitwise tests during refactoring

Checklist for merging

• Updated changelog entry
• Documentation updated
• Update conf.py

Checklist for release

• Merge into main
• Create release from the main branch with appropriate tag
• Delete feature-branch

Testing Datasets

• Dataset needed for testing available upon request
• Dataset download instructions included
• No dataset needed

[hkershaw-brown]

For un reviewed atmos-chem forward operators see #743