[DAR-2639][External] Add data & tests for in-platform model training

[JBWilkie]

Problem

There are no tests for in-platform model training functionality

Solution

Add data & tests to support testing of darwin-py functionality used in in-platform model training. In addition to this:

• 1: Re-add a function convert_xyxy_to_bounding_box used by model training
• 2: Force get_annotations() to read local items from the item name, not the annotation file name

Changelog

(Will appear in release docs)

[linear[bot]]

DAR-2639 Add data & tests for in-platform model training