add coupled unsteady problem and solver

[JonahJ27]

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[codecov]

Codecov Report

❌ Patch coverage is 92.34450% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.73%. Comparing base (5f14b81) to head (037db55).

Files with missing lines	Patch %	Lines
...are/coupled_unsteady_ring_vortex_lattice_method.py	91.92%	13 Missing ⚠️
pterasoftware/_core.py	71.42%	2 Missing ⚠️
...erasoftware/unsteady_ring_vortex_lattice_method.py	87.50%	1 Missing ⚠️

Additional details and impacted files

@@                 Coverage Diff                 @@
##           class_structure     #161      +/-   ##
===================================================
+ Coverage            91.70%   91.73%   +0.02%     
===================================================
  Files                   34       35       +1     
  Lines                 6752     6953     +201     
===================================================
+ Hits                  6192     6378     +186     
- Misses                 560      575      +15     

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[camUrban]

Thanks for taking the new class structure for a test drive. Good to see the foundation works for the aeroelastic use case.

A couple of things before we move forward:

1. This PR will auto-close once I merge Refine class structure #160 and delete the class_structure branch. Your commits stay on your fork, so you can cherry-pick from coupled_unsteady_addition into [FEATURE] Add structural aeroelasticity #156 after you update it from main.
2. When you port this into [FEATURE] Add structural aeroelasticity #156, I think we should rework it a bit. The direction I landed on in Refine class structure #160 was to have the feature variants extend the Core* classes directly as siblings of the standard classes, rather than going through an intermediate Coupled* layer. Part of the reasoning is that CoupledUnsteadyProblem's base initialize_next_problem ends up regenerating from the movement, which is what UnsteadyProblem.__init__ already does, so the middle layer doesn't carry much weight on its own. Using Aeroelastic* naming also makes it clearer what the coupling is to. Happy to walk through all this at our next 1:1!

Nice work validating the design.