Adopt XS containers everywhere (incomplete work)

lib/Slic3r/Fill/Rectilinear.pm

@@ -67,7 +67,7 @@ sub fill_surface {
     # are kept even if the expolygon has vertical sides
     my @paths = @{ Boost::Geometry::Utils::polygon_multi_linestring_intersection(
         +($expolygon->offset_ex(scaled_epsilon))[0]->pp,  # TODO: we should use all the resulting expolygons and clip the linestrings to a multipolygon object
-        [ @{ $self->cache->{$cache_id} } ],
+        [ map $_->pp, @{ $self->cache->{$cache_id} } ],
     ) };
     
     # connect lines