Added surface area constraint function to pyGeo MPhys wrapper

[eytanadler]

Purpose

There was no surface area constraint function in the MPhys wrapper for DVCon. Now there is.

Expected time until merged

A few days

Type of change

• [ ] Bugfix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (non-backwards-compatible fix or feature)
• [ ] Code style update (formatting, renaming)
• [ ] Refactoring (no functional changes, no API changes)
• [ ] Documentation update
• [ ] Maintenance update
• [ ] Other (please describe)

Testing

When setting up the geometric constraints in an MPhys problem, call something like self.geometry.nom_addSurfaceAreaConstraint("surface_area") to add a geometry output that computes the surface area of the constraint surface. It works in my scripts.

Checklist

• [ ] I have run flake8 and black to make sure the Python code adheres to PEP-8 and is consistently formatted
• [ ] I have formatted the Fortran code with fprettify or C/C++ code with clang-format as applicable
• [ ] I have run unit and regression tests which pass locally with my changes
• [ ] I have added new tests that prove my fix is effective or that my feature works
• [ ] I have added necessary documentation

[codecov[bot]]

Codecov Report

Attention: 6 lines in your changes are missing coverage. Please review.

Comparison is base (7043a74) 65.32% compared to head (efe6af1) 65.30%.

Files	Patch %	Lines
pygeo/mphys/mphys_dvgeo.py	0.00%	6 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #237 +/- ## ========================================== - Coverage 65.32% 65.30% -0.02% ========================================== Files 47 47 Lines 12121 12124 +3 ========================================== Hits 7918 7918 - Misses 4203 4206 +3 ```

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