Fix: Use faiss/impl/AuxIndexStructures.h for RangeSearchResult

RangeSearchResult is defined in faiss/impl/AuxIndexStructures.h,
not in utils/Heap.h or utils/distances.h. This is the correct
header for RangeSearchResult definition in FAISS.

Author: anupammaurya6767

src/cpp/faiss_index.cpp

@@ -8,7 +8,7 @@
 #include <faiss/index_factory.h>
 #include <faiss/index_io.h>
 #include <faiss/impl/io.h>
-#include <faiss/utils/Heap.h>
+#include <faiss/impl/AuxIndexStructures.h>
 #include <fstream>
 #include <sstream>
 #include <cstdio>