Refactored raw data loading process

src/ptbench/configs/datasets/__init__.py

src/ptbench/configs/datasets/shenzhen/__init__.py

src/ptbench/configs/datasets/shenzhen/default.py

src/ptbench/configs/models/pasa.py

src/ptbench/data/__init__.py

src/ptbench/data/base_datamodule.py

src/ptbench/data/dataset.py

src/ptbench/data/loader.py

src/ptbench/data/sample.py

src/ptbench/data/shenzhen/__init__.py

src/ptbench/data/shenzhen/default.py

src/ptbench/data/shenzhen/rgb.py

src/ptbench/data/utils.py

src/ptbench/engine/predictor.py

src/ptbench/models/pasa.py

src/ptbench/scripts/train.py