Free G4World's G4Volume wrappers; forbid copy/move to avoid double-free

G4World stored raw G4Volume* wrappers in g4volumesMap but had no
destructor, so every g4world.reset() on geometry reload leaked one
wrapper per volume — unbounded growth in long interactive sessions.

Add a destructor that deletes the wrappers (Geant4 owns the contained
solid/logical/physical objects, so only the lightweight GEMC wrappers are
freed). Because G4World previously inherited GBase's defaulted copy/move,
adding an owning destructor would make a shallow copy double-free; G4World
is only ever held by shared_ptr, so delete copy and move to forbid
relocation. Verified the deletions don't break the build (nothing copies
or moves G4World).

Fixes #135

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: zhaozhiwen

gemc/g4system/g4world.h

@@ -63,6 +63,19 @@ class G4World : public GBase<G4World>
 	 */
 	G4World(const GWorld* gworld, const std::shared_ptr<GOptions>& gopts);
 
+	/// Frees the owned G4Volume wrappers. Geant4 owns the contained solid/logical/physical
+	/// objects, so only the lightweight wrappers allocated by the object factories are deleted.
+	~G4World() {
+		for (auto& [name, vol] : g4volumesMap) { delete vol; }
+	}
+
+	// G4World now owns the raw G4Volume* wrappers (freed in the destructor). It is only ever held
+	// by shared_ptr, so forbid copy/move to avoid a shallow copy double-freeing the wrappers.
+	G4World(const G4World&)            = delete;
+	G4World& operator=(const G4World&) = delete;
+	G4World(G4World&&)                 = delete;
+	G4World& operator=(G4World&&)      = delete;
+
 	// ────── lookup / mutators ────────────────────────────────────────
 
 	/**