Design Results class to encapsulate model prediction results.

[macks22]

This will eventually hold a variety of methods currently available as functions in the scaffold module. These include:

1. quantitative evaluation methods: compute_error, eval_results, rmse, mae, etc.
2. cold-start identify, remove, and summarize methods
3. plotting methods: such as granular_eval
4. save/load methods: should save model learned, predictions made, and known targets necessary for eval; might also save exact datasets used (after pre-processing, filtering, etc.) or just some information necessary to replicate the datasets.
5. eval formatting methods: such as results_to_table