fix(staging): handle CheckBox and TableChunk in convert_to_coco
Root cause
convert_to_coco() builds its category list only from TYPE_TO_TEXT_ELEMENT_MAP and looks up each annotation's id with [x["id"] for x in categories if x["name"] == el["type"]][0]. TableChunk is intentionally kept out of that map (see the comment in elements_from_dicts()), and CheckBox is not in it either, so both raise IndexError. This happens, for example, on chunked output that contains a split table.
Change
Append CheckBox and TableChunk categories after the sorted mapped types. Ids are positional, so every existing category id is unchanged.
Tests
New test_convert_to_coco_handles_element_types_outside_the_text_element_map: it checks that the category list is the mapped types followed by the two new ones, and that each annotation gets the right id. It raises IndexError before the change and passes after it. test_unstructured/staging passes locally.
AI assistance was used to prepare this change; I reviewed and tested it.