Shape function gradients are incorrectly assumed to be constant within wedge elements

Description

In Code/Source/solver/nn_elem_props.h, the flag mshType::lshpF is set to indicate whether shape functions are linear (including wedge elements). This flag is then used in several places throughout the code to decide whether the derivative of the shape functions is constant across the element or needs to be computed per Gauss point. This is true for LIN1, TRI3, and TET4 elements but not for WDG elements.

for (int g = 0; g < lM.nG; g++) {
  if (g == 0 || !lM.lShpF) {
    nn::gnn(eNoN, nsd, nsd, Nx_g, xl, Nx, Jac, ksix);   // Nx and Jac
  }
  double w = lM.w(g) * Jac;
  ...
}

This bug appears 35 times in the codebase, and there are currently no wedge element test cases to catch it.

Reproduction

There are no wedge element test cases to reproduce this bug.

Expected behavior

Either a new flag should be added to indicate that an element has a constant shape function gradient or these locations in the code should be gated on element type rather than lshpF

Additional context

No response

Code of Conduct

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Start in Code/Source/solver/nn_elem_props.h to understand how mshType::lshpF is set for WDG elements. Review the listed call sites in post.cpp, fluid.cpp, fsi.cpp, and the other named files, then add wedge-element test coverage; done means wedge gradients and Jacobians are handled correctly at each Gauss point.