added saliency map evaluation and visualisation for lightning models

src/ptbench/engine/saliencymap_evaluator.py

src/ptbench/engine/visualizer.py

src/ptbench/scripts/calculate_road.py

src/ptbench/scripts/evaluate_saliencymaps.py

src/ptbench/scripts/generate_saliencymaps.py

src/ptbench/scripts/visualize.py

src/ptbench/utils/cam_utils.py