Add TEOS-10 and z-tilde vertical coordinate

[xylar]

This pull request introduces a modular and extensible Equations of State (EOS) framework for the Polaris ocean model, enabling support for both linear and TEOS-10 EOS options. It adds new high-level APIs for computing seawater density and specific volume, improves documentation, and refactors vertical coordinate handling for clarity and extensibility.

This merge also adds a module for the z-tilde vertical coordinate in Omega. Functionality is available for computing geometric pressure from pseudo-height and vice versa, as pressure from geometric thickness, geometric height from pseudo-height, and finally pressure and specific volume together from temperature and salinity values at specified locations in geometric height.

In addition, this merge includes performance improvements and clean-up to the z-star and z-level vertical coordinate initialization.

Checklist

• 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]

Testing

I ran both the Omega and MPAS-Ocean PR suites on Chrysalis with Intel, using main as a baseline.

For Omega, I am seeing diffs in manufactured solution del4 (again!) that I can't yet explain. All other tests are BFB.

For MPAS-Ocean, I am seeing machine-precision diffs in the initial conditions for in the ice_shelf_2d/5km/z-star test and overflow/default, and BFB results for all other tests.

[xylar]

I believe my diffs are just a mistake in the Omega version I was using as the baseline. I have re-initialized the Omega submodule and now see no differences in my omega.yml files (baseline compared with this branch), whereas i saw diffs earlier. I'll update soon...

[xylar]

Rerunning the Omega PR suite with the correct baseline Omega submodule shows bit-for-bit results for all tests.

[xylar]

@cbegeman, would you have time to give this a quick look? My hope is that this will be helpful to you as well, but we may have some conflicts with other work to untangle after this goes in.

[xylar]

I think it would make sense for this to go in before #460 but we should discuss that.

[cbegeman]

Approving on the basis of code inspection and @xylar 's testing. I have tested a subset of the z-tilde routines from this PR in another branch. Thanks!