[abhiyanpaudel]

Adds LinearCubicWedgeShape, a 12-node wedge that is linear in $(\xi_0, \xi_1)$ and cubic Lagrange in $\zeta$, for field-aligned wedge geometry. Depends on #113.

$$ N_a = L_a,\ell_0, \quad N_{a+3} = L_a,\ell_3, \quad N_{6+2a} = L_a,\ell_1, \quad N_{7+2a} = L_a,\ell_2, \qquad a = 0, 1, 2 $$

Here $\ell_k$ are the cubic Lagrange polynomials on $\zeta = -1, -\tfrac13, \tfrac13, 1$. Nodes 0–5 are the vertices, and nodes $6+2a$ and $7+2a$ sit on vertical edge $a$ at $\zeta = \mp\tfrac13$.

Changes

• src/MeshField_Shape.hpp: add LinearCubicWedgeShape
• test/testCubicWedgeShape.cpp (new): Kronecker delta, partition of unity, exact reproduction of $\mathrm{span}\lbrace 1, \xi_0, \xi_1 \rbrace \times \lbrace 1, \zeta, \zeta^2, \zeta^3 \rbrace$ and gradients check
• CMakeLists.txt: register CubicWedgeShapeTest