rect - need to be able to coalesce rectangles

[howff]

First use case is the rectangles generated by running OCR at multiple scales of the same image - you often get multiple very similar (but not exactly the same) rectangles. The coordinates will be off by 2 pixels but sometimes by 4 pixels.

These can be merged to the largest bounding box except that

• DicomRect - need to check they are the same frame and overlay
• DicomRectText - need to compare the text strings (see https://pypi.org/project/fastDamerauLevenshtein/) and maybe pick the longest if they are very similar or just keep both rectangles otherwise