add box_aspect_ratio property to sv.Detections

[SkalskiP]

Description

This pull request refactors how aspect ratios for bounding boxes are calculated and accessed in the codebase. The main change is the removal of the standalone box_aspect_ratio utility function, which is now replaced by a new box_aspect_ratio property on the Detections class.

import numpy as np
import supervision as sv

xyxy = np.array([
    [10, 10, 50, 50],
    [60, 10, 180, 50],
    [10, 60, 50, 180],
])

detections = sv.Detections(xyxy=xyxy)

detections.box_aspect_ratio
# array([1.0, 3.0, 0.33333333])

ar = detections.box_aspect_ratio
detections[(ar < 2.0) & (ar > 0.5)].xyxy
# array([[10., 10., 50., 50.]])