perf(hex8): defer optional paired tangent until a valid linear trial

src/fesa/elements/hex8_element.cpp

@@ -7,6 +7,7 @@
 
 #include "../math/dense_blas_internal.h"
 #include "hex8_geometry.h"
+#include "hex8_linear_tangent_cache.h"
 
 namespace fesa {
 namespace {
@@ -116,7 +117,9 @@ Hex8Element::Hex8Element(EntityIndex index, ElementDofLayout layout,
       kappa_{kappa},
       mu_{mu},
       density_{density},
-      location_{std::move(location)} {}
+      location_{std::move(location)},
+      paired_linear_tangent_{
+          std::make_shared<hex8_internal::LinearTangentCache>()} {}
 
 Status Hex8Element::Failure(const char* message) const {
   return Status::Failure(FailureCategory::kModel,
@@ -273,13 +276,6 @@ Result<Hex8Element> Hex8Element::Create(EntityIndex index,
   if (backend_inputs_failed)
     return Result<Hex8Element>::Failure(candidate.Failure(
         "Hex8 dense MKL operands failed finite validation."));
-  const Vector zero{24U};
-  const auto paired = candidate.EvaluateHighLow(zero, zero, false);
-  if (paired.HasValue()) {
-    candidate.paired_linear_tangent_high_ = paired.Value().high.tangent;
-    candidate.paired_linear_tangent_low_ = paired.Value().tangent_low;
-    candidate.paired_linear_tangent_ready_ = true;
-  }
   return Result<Hex8Element>::Success(std::move(candidate));
 }