feat: allow custom material for grid overlay, and material creation from Uint8List

thermion_dart/lib/src/viewer/src/thermion_viewer_base.dart

@@ -765,7 +765,7 @@ abstract class ThermionViewer {
   ///
   ///
   ///
-  Future showGridOverlay();
+  Future showGridOverlay({covariant Material? material});
 
   ///
   ///
@@ -788,6 +788,11 @@ abstract class ThermionViewer {
   ///
   Future destroyTexture(covariant ThermionTexture texture);
 
+  ///
+  ///
+  ///
+  Future<Material> createMaterial(Uint8List data);
+
   ///
   ///
   ///