use rectangles to find the squares

We know that the cards are rectangles of a certain ratio, however again because of the skewing it might not be totally accurate, but approximately. So find all rectangles with that ratio and then take convex hull as the mask. _Should be good._

Start by locating the notebook cell or entry point that currently detects cards or squares; the issue names no file or test. Use the cards’ approximate rectangle ratio and verify that the resulting convex hull produces the intended mask.

Written by the indexing model from the issue text.