* fix(detection): make Detections.area OBB-aware
When detections carry ORIENTED_BOX_COORDINATES (the four xyxyxyxy corners),
the area property returned the area of the derived axis-aligned bounding
box instead of the rotated body. The AABB overestimates by up to ~2x for a
45-degree rotation, which silently miscomputes downstream values — most
visibly the area-sorted z-ordering inside MaskAnnotator / HaloAnnotator,
and any user code that filters detections by area.
* docs(detection): use string literal in Detections.area doctest
* test(detection): single-line docstring on test_uses_oriented_box_corners_when_present
* fix(detection): validate (N,4,2) shape of OBB data field in Detections.area
* perf(detection): replace np.roll pair with cross-diagonal shoelace in Detections.area
* perf(detection): cast x/y slices to float64 instead of full corners array
* refactor(detection): extract obb_polygon_area to detection/utils/boxes.py
* test(detection): add test_raises_on_malformed_obb_coordinates_shape
* test(detection): assert per-branch dtype contract for Detections.area
* docs(detection): document OBB dispatch contract and dtype in Detections.area docstring
---------
Co-authored-by: Jirka Borovec <6035284+Borda@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
Co-authored-by: claude[bot] <209825114+claude[bot]@users.noreply.github.com>
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