Task 3.4 - Step 4: Build ML experiment pipeline

Branch: step-4-build-ml-pipeline

Tasks:

- [ ] create `src/stages` directory
- [ ] create `.py` modules for each pipeline stage:

- data_load.py
- data_split.py
- featurize.py
- train.py
- evaluate.py
- [ ] run each stage

Requirements:
- use `params.yaml` to manage stages configuration