fem: pyramid5 element (solver, quality, decks, VTK)

A five-node pyramid, the conforming transition between a hexahedron's face
and tetrahedra: Bedrosian's rational shape functions with a collapsed (Duffy)
Gauss rule, a certified Jacobian on the base square with exact volume, a
scaled Jacobian, C3D5 / CPYRAM / LS-DYNA degenerate solid, VTK_PYRAMID and
the binary mesh code 13. A distorted hex8-pyramid5-tet4 transition mesh
passes the patch test and uniaxial tension exactly.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

docs/fem.md

@@ -76,7 +76,8 @@ rational pyramid, 2 for the quadratic ones).
 Evaluation at a natural point `xi: [f64; 3]` (unused coordinates are zero):
 
 - `eval(xi) -> Shape`: values `n` and first derivatives `dn[i] = ∂Nᵢ/∂(ξ, η, ζ)`. tet4, tet10,
-  wedge6, hex8, hex20 use the hand-written functions of `shape.rs` (the solid kernels' path).
+  wedge6, hex8, hex20 use the hand-written functions of `shape.rs` (the solid kernels' path);
+  the solid kernel's pyramid5 uses this module's.
 - `eval2(xi) -> Shape2`: adds `d2n[i][a][b] = ∂²Nᵢ/∂ξₐ∂ξ_b`, from second-order forward-mode
   automatic differentiation of the same formulas (`jet::Jet`): exact to round-off.
 - `gradients(&shape, xyz) -> Gradients`: physical `dx[i] = ∇ₓNᵢ = J⁻¹ ∇_ξNᵢ` and `det J`, with