Linear vs Ridge vs Lasso with cross-validation

Build a pipeline to compare Linear, Ridge, and Lasso.
Tune hyperparameters for Ridge and Lasso with 5-fold CV, then report mean CV score and final test metrics for all three models.

No file or test is named in the issue. Start by locating the existing notebook and the current data/model entry point, then run the present workflow; done means Linear, tuned Ridge, and tuned Lasso are compared with 5-fold CV, with mean CV scores and final test metrics reported for each.

Written by the indexing model from the issue text.