Clean up TODOs and comments after refactor

[iamyifan]

• Update comments in config.py with new BabyJoeyDataset and BabyJoeyDataloader paths.
• Change all paths in config.py from relative paths to full paths.
• Clean and add comments and TODOs in main.py.
• Update function documentation for BabyJoeyDataset in src/data/data.py
• Change default sample_ratio to 1 in src/data/data.py (i.e., use the full dataset by default).
• Remove unnecessary imports (for type hint) in src/util/utils.py
• Change hard-coded random.seed(42) to random.seed(seed) in BabyJoeyUtil.sample_dataset in src/util/utils.py.