[FEATURE] Speed up creating UnsteadyProblems

[camUrban]

Problem Statement

Since v4.0.0, several users have reported that Ptera Software has become much slower at creating UnsteadyProblems. I've also noticed this, and it is particularly bad when initializing problems with many time steps.

Proposed Solution

More investigating needs to be done to pinpoint the exact cause of the slowdown. However, I suspect it may have something to do with recomputing property attributes in Airplane or Wing.

It's also possible that we are unnecessarily calling parameter validation functions on arguments in private methods and functions.

One last thing to try is using defining __slots__ for Airfoil, WingCrossSection, Wing, and Airplane, which will likely provide a modest speed up for attribute assignment and access.

Alternative Solutions

None

Additional Context

None

[camUrban]

I'll close this issue upon merge of #93, which speeds up UnsteadyProblem creation by caching non-changing property values and deep-copying mesh data for cases with identical geometry. The performance gains are typically about 8-10x, with the most dramatic improvements (up to 40x!) for very large UnsteadyProblems with fine meshes and many time steps.

Because of the large gains, I decided to not implement __slots__ or look too deeply for unnecessary parameter validation. However, these would likely provide further performance gains. We should investigate these paths further in the future if we end up needing even faster problem creation.