A region reported with a smart event, from <DetectionRegionList>.
An NVR relaying an AcuSense camera posts one <DetectionRegionEntry> per
region that fired, with <regionID>, a <RegionCoordinatesList> that may
be empty, the <TargetRect> of what was seen and the <detectionTarget>.
optional
id: number
<regionID>, when present. Rules count from 0 here, from 1 in smart/rules.ts.
optional
sensitivityLevel: number
<sensitivityLevel>, when present.
coordinates: Point[]
The region's corners, from <RegionCoordinatesList>; [] when the list is empty.
detectionTarget: string[]
<detectionTarget> split on commas, such as ["human"].
optional
targetRect: TargetRect
The box around what was detected, from <TargetRect>, when present.