refactor using pimpl and fix test

src/Math/VoxImage.h

@@ -109,8 +109,20 @@ public:
 
   VoxImage(const Vector3i &size);
 
-  VoxImage(const VoxImage<T> &copy) : BaseClass(copy) {
-    this->m_Data = copy.m_Data;
+  // Use compiler-generated copy constructor and assignment operator
+
+  VoxImage<T>& operator=(const VoxImage<T>& other) {
+    if (this != &other) {
+      // Copy the base class non-virtual parts (dims, spacing, position, etc.)
+      // WITHOUT going through the virtual SetDims chain (which would call
+      // m_Data.resize() THEN DataAllocator::operator= will resize again → double-free).
+      // Instead, directly copy DataAllocator and update the StructuredGrid state.
+      this->m_Data = other.m_Data;
+      StructuredGrid::SetDims(other.GetDims());
+      this->SetSpacing(other.GetSpacing());
+      this->SetPosition(other.GetPosition());
+    }
+    return *this;
   }
 
   inline DataAllocator<T> &Data() { return this->m_Data; }