[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

src/constants_inf.pxd

@@ -1,6 +1,7 @@
 cdef str CONFIG_FILE
 
 cdef str AI_ONNX_MODEL_FILE
+cdef str INT8_CALIB_CACHE_FILE
 
 cdef str CDN_CONFIG
 cdef str MODELS_FOLDER