Integrate Refactor solver sources and dual MSVC CMake builds

src/fesa/elements/hex8_high_low.cpp

@@ -8,7 +8,6 @@
 #include "../math/high_low_arithmetic.h"
 #include "hex8_geometry.h"
 #include "hex8_linear_tangent_cache.h"
-#include "hex8_pair_arithmetic.h"
 #include "hex8_pair_simd.h"
 
 namespace fesa {
@@ -18,13 +17,13 @@ using Triple = std::array<HighLow, 3>;
 using Tensor = std::array<Triple, 3>;
 
 HighLow operator+(HighLow a, HighLow b) {
-  return hex8_internal::AddPair(a, b);
+  return math_internal::Add(a, b);
 }
 HighLow operator-(HighLow a, HighLow b) {
   return math_internal::Subtract(a, b);
 }
 HighLow operator*(HighLow a, HighLow b) {
-  return hex8_internal::MultiplyPair(a, b);
+  return math_internal::Multiply(a, b);
 }
 HighLow operator/(HighLow a, HighLow b) {
   return math_internal::Divide(a, b);