[montgomery_shenzhen_indian] Refactor aggregated dataset

pyproject.toml

src/ptbench/data/mc_ch_in/__init__.py

src/ptbench/data/mc_ch_in/default.py

src/ptbench/data/mc_ch_in/fold_0.py

src/ptbench/data/mc_ch_in/fold_1.py

src/ptbench/data/mc_ch_in/fold_2.py

src/ptbench/data/mc_ch_in/fold_3.py

src/ptbench/data/mc_ch_in/fold_4.py

src/ptbench/data/mc_ch_in/fold_5.py

src/ptbench/data/mc_ch_in/fold_6.py

src/ptbench/data/mc_ch_in/fold_7.py

src/ptbench/data/mc_ch_in/fold_8.py

src/ptbench/data/mc_ch_in/fold_9.py

src/ptbench/data/montgomery_shenzhen_indian/__init__.py

src/ptbench/data/montgomery_shenzhen_indian/datamodule.py

src/ptbench/data/montgomery_shenzhen_indian/default.py

src/ptbench/data/montgomery_shenzhen_indian/fold_0.py

src/ptbench/data/montgomery_shenzhen_indian/fold_1.py

src/ptbench/data/montgomery_shenzhen_indian/fold_2.py

src/ptbench/data/montgomery_shenzhen_indian/fold_3.py