tone-check: refactor retraining image and script for DAG integration

• pinned python dependencies for reproducibility
• optimized blubberfile to keep it DRY
• removed config.py and made args configurable in retrain.py
• updated retrain_unit_test.py to work with refactored retrain.py

This change can be tested locally by building the image, running the container with data files from T396495#11114843, and executing the retrain script with appropriate arguments. For example:

python training/tone_check/retrain/retrain.py \
--training-data-path "/srv/edit_check/my_test/upload/data/peacock_detection_dataset.csv" \
--output-model-path "/srv/edit_check/my_test/upload/output" \
--base-model-path "/srv/edit_check/my_test/upload/base_model"

Bug: T401007