Query is nothing else than a std::optional but just came earlier

• Turn query into an std::optional. For now let's keep the extra methods but should be phased out on a longer term
• Add the volumeId as attribute of the getChildrenWithTrf return structs
• Add sorter struct to classify two materials as equivalent.

GeoModelCore/GeoModelHelpers/GeoModelHelpers/GeoMaterialSorter.h

+/*
+  Copyright (C) 2002-2024 CERN for the benefit of the ATLAS collaboration
+*/
+#ifndef GeoModelHelpers_GeoMaterialSorter_H
+#define GeoModelHelpers_GeoMaterialSorter_H
+
+#include "GeoModelKernel/GeoMaterial.h"
+#include "GeoModelKernel/GeoElement.h"
+#include "GeoModelKernel/GeoIntrusivePtr.h"
+#include <set>
+
+/// @brief  Helper struct to deuplicate equivalent materials with different naming
+struct GeoMaterialSorter {
+    /** @brief Comparison operator returing whether Material A is smaller than Material B */
+    bool operator()(const GeoMaterial* a, const GeoMaterial* b) const;
+    /** @brief Comparison operator returing whether the Element A is smaller than Element B */
+    bool operator()(const GeoElement* a, const GeoElement* b) const;
+    /// @brief Compares 2  GeoMaterials
+    /// @param a : Pointer to material A
+    /// @param b : Pointer to material B
+    /// @return  Returns 0 if no defining material property could be found that differs
+    ///          Returns -1 if the first defining & differing property of A is smaller
+    ///          Returns 1 otherwise
+    int compare(const GeoMaterial* a, const GeoMaterial* b) const;
+    int compare(const GeoElement* a, const GeoElement* b) const;
+
+};
+
+/// @brief 
+/// @tparam ShapeType 
+using GeoMaterialSet = std::set<GeoIntrusivePtr<const GeoMaterial>, GeoMaterialSorter>;
+
+#endif
\ No newline at end of file