Update rectangular (box) configurations

[apcraig]

PR checklist

• Short (1 sentence) summary of your PR:
  Update rectangular (box) configurations
• Developer(s):
  apcraig
• Suggest PR reviewers from list in the column to the right.
• Please copy the PR test results link or provide a summary of testing completed below.
  Several box tests change answers, as expected. This fixes a few bugs in the box setup. Non-box configurations pass and are bit-for-bit as expected. https://github.com/CICE-Consortium/Test-Results/wiki/cice_by_hash_forks#c3429c9a8f34869800e2ef8d06a2096be89d1d0e
• How much do the PR code changes differ from the unmodified code?
  • bit for bit
  • different at roundoff level
  • more substantial, but just for some box configurations
• Does this PR create or have dependencies on Icepack or any other models?
  • Yes
  • No
• Does this PR update the Icepack submodule? If so, the Icepack submodule must point to a hash on Icepack's main branch.
  • Yes
  • No
• Does this PR add any new test cases?
  • Yes
  • No
• Is the documentation being updated? ("Documentation" includes information on the wiki or in the .rst files from doc/source/, which are used to create the online technical docs at https://readthedocs.org/projects/cice-consortium-cice/. A test build of the technical docs will be performed as part of the PR testing.)
  • Yes
  • No, does the documentation need to be updated at a later time?
    • Yes
    • No
• Please document the changes in detail, including why the changes are made. This will become part of the PR commit log.

Update the rectangular (box) grid configurations.

• Fix bug where left hand side of rectangular grids had incorrect longitudes and latitudes computed. This changes answers in some box configurations.
• Update the box resolutions. dxrect and dyrect were hardwired to 30km for all box resolutions. Now adjust dxrect and dyrect depending on the number of gridcells so it always covers an area of about 3 degrees by 3 degrees. This means gbox12 is 30km resolution, gbox80 is 5km, gbox128 is 3 km, and gbox180 is 2 km. Reduce the gbox180 timestep to 1800s for stability. This changes answers for some box configurations.
• Remove u masking from box2001 ocean forcing, bit-for-bit.
• Remove 50W check associated with box2001 initial conditions, bit-for-bit.
• Add rectangular grid diagnostics
• Minor update to the box2001 documentation

Explicitly set npt_unit in all set_nml files that have npt set. Improves robustness where one option sets npt and another sets npt_unit.

These changes do not fundamentally change how the model behaves with simple box test configurations. This just fixes a few inconsistencies in how the box grids are setup.

Closes #1004

[dabail10]

This looks good. Thanks for chasing this down.