[scripts] Streamline saliency map generation and analysis

src/ptbench/data/datamodule.py

src/ptbench/engine/saliency/generator.py

src/ptbench/engine/saliency/interpretability.py

src/ptbench/scripts/experiment.py

src/ptbench/scripts/predict.py

src/ptbench/scripts/saliency/completeness.py

src/ptbench/scripts/saliency/generate.py

src/ptbench/scripts/saliency/interpretability.py

src/ptbench/utils/checkpointer.py

tests/test_cam_utils.py