use listview.builder for optimization

[HasanAlqaisi]

From flutter docs:

The standard ListView constructor works well for small lists. To work with lists that contain a large number of items, it’s best to use the ListView.builder constructor.

In contrast to the default ListView constructor, which requires creating all items at once, the ListView.builder() constructor creates items as they’re scrolled onto the screen.

So I changed listview to listview.builder for better performance.