[AZ-180] Add Jetson Orin Nano support with INT8 TensorRT engine

- Dockerfile.jetson: JetPack 6.x L4T base image (aarch64), TensorRT and PyCUDA from apt
- requirements-jetson.txt: derived from requirements.txt, no pip tensorrt/pycuda
- docker-compose.jetson.yml: runtime: nvidia for NVIDIA Container Runtime
- tensorrt_engine.pyx: convert_from_source accepts optional calib_cache_path; INT8 used when cache present, FP16 fallback; get_engine_filename encodes precision suffix to avoid engine cache confusion
- inference.pyx: init_ai tries INT8 engine then FP16 on lookup; downloads calibration cache before conversion thread; passes cache path through to convert_from_source
- constants_inf: add INT8_CALIB_CACHE_FILE constant
- Unit tests for AC-3 (INT8 flag set when cache provided) and AC-4 (FP16 when no cache)

Made-with: Cursor

docker-compose.jetson.yml

@@ -0,0 +1,20 @@
+name: detections-jetson
+
+services:
+  detections:
+    build:
+      context: .
+      dockerfile: Dockerfile.jetson
+    ports:
+      - "8080:8080"
+    runtime: nvidia
+    environment:
+      LOADER_URL: ${LOADER_URL}
+      ANNOTATIONS_URL: ${ANNOTATIONS_URL}
+    env_file: .env
+    volumes:
+      - detections-logs:/app/Logs
+    shm_size: 512m
+
+volumes:
+  detections-logs: