[Feature] Add `Column` object(s) to `find_table()`

[Pk13055]

Currently, find_table returns a table object that contains two props, viz. .cells: list[tuple(float, float, float, float]] and .rows: Row object, which in turn contains .cells. It would be great if, similar to .rows, a .columns property is also added, since intersections of bboxes can be calculated and thereby external OCR can be applied on a per-cell basis.