fix includes for Windows

Author: nmwsharp

include/polyscope/sparse_volume_grid.h

@@ -13,6 +13,7 @@
 #include "polyscope/sparse_volume_grid_scalar_quantity.h"
 
 #include <cstdint>
+#include <numeric>
 #include <vector>
 
 namespace polyscope {

include/polyscope/sparse_volume_grid.ipp

@@ -2,8 +2,6 @@
 
 #pragma once
 
-#include "polyscope/utilities.h"
-
 namespace polyscope {
 
 inline uint64_t SparseVolumeGrid::nCells() const { return occupiedCellsData.size(); }