Add engines::ZedNative class wrapping ZED SDK's TensorRT-optimized
object detection. On every frame grab, detected objects (label,
confidence, 3D position, 2D/3D bounding boxes) are serialized as a
flat float32 array and sent as a new "objects" dora output with
frame_id correlation to image_bgr.
Extract shared env-var helpers into src/util/env.h and expose
sl::Camera& via Camera::handle() for engine access.
Closes#3
Extract camera lifecycle (open, warmup, grab, close) and
environment-based configuration into src/zed/camera.{h,cc}.
Thin main.cc now only handles the dora event loop.
Closes#2
cristhian aguilera