[AZ-171] Add TensorRT tests, AC coverage gate in implement skill, optimize test infrastructure

- Add TensorRT export tests with graceful skip when no GPU available
- Add AC test coverage verification step (Step 8) to implement skill
- Add test coverage gap analysis to new-task skill
- Move exported_models fixture to conftest.py as session-scoped (shared across modules)
- Reorder tests: e2e training runs first so images/labels are available for all tests
- Consolidate teardown into single session-level cleanup in conftest.py
- Fix infrastructure tests to count files dynamically instead of hardcoded 20

Made-with: Cursor

tests/test_infrastructure.py

@@ -3,12 +3,14 @@ import constants as c
 
 def test_fixture_images_dir_has_jpegs(fixture_images_dir):
     jpgs = list(fixture_images_dir.glob("*.jpg"))
-    assert len(jpgs) == 20
+    assert len(jpgs) > 0
 
 
-def test_fixture_labels_dir_has_yolo_labels(fixture_labels_dir):
+def test_fixture_labels_dir_has_yolo_labels(fixture_labels_dir, fixture_images_dir):
     txts = list(fixture_labels_dir.glob("*.txt"))
-    assert len(txts) == 20
+    jpgs = list(fixture_images_dir.glob("*.jpg"))
+    assert len(txts) > 0
+    assert len(txts) == len(jpgs)
 
 
 def test_fixture_onnx_model_bytes(fixture_onnx_model):