Add SO and RRS meshes

[xylar]

These are the SO12to30 and RRS6to18 meshes for now. They are intended to be a starting point for designing E3SM v4 RRMs and to make sure we have example workflows in Polaris that support RRMs. Before this PR, all spherical meshes were constant resolution and there were some built-in restrictions related to that. With this PR, support for variable-resolution meshes with a min and max resolution are supported.

Checklist

• User's Guide has been updated
• Developer's Guide has been updated
• API documentation in the Developer's Guide (api.md) has any new or modified class, method and/or functions listed
• Documentation has been built locally and changes look as expected
• Testing comment in the PR documents testing used to verify the changes

[xylar]

Documentation is still needed.

[xylar]

Testing

I ran the e3sm/init/so12to30km/topo/cull and e3sm/init/rrs6to18km/topo/cull on Chrysalis:

/lcrc/group/e3sm/ac.xylar/polaris_0.8/chrysalis/test_20250814/cull_so_rrs

[xylar]

I'm going to merge this without a review for now because I think there will be plenty of time to look over it in more detail as we flesh out the workflow. For now, these just serve as 2 examples of variable resolution meshes, ported from Compass.