readPoiData method
Reads POI data for a rectangular area defined by corner tiles.
Combines POI data from all tiles within the specified area.
Precondition: upperLeft.tileX <= lowerRight.tileX && upperLeft.tileY <= lowerRight.tileY
upperLeft Upper-left corner tile of the requested area
lowerRight Lower-right corner tile of the requested area
Returns combined POI data for the area
Implementation
@override
Future<DatastoreBundle> readPoiData(Tile upperLeft, Tile lowerRight) {
// TODO: implement readPoiData
throw UnimplementedError();
}