Remove value-tuples from the public surface of the API #2501
Description
The public surface of the API contains value-tuples, which present a few problems:
- We can't change the data we return in future releases (e.g. add functionality)
- They don't play well with F#
- Support in VS isn't great
These occur are in at least
CrossValidation(e.g. for each task)TrainTestSplit: (e.g. for each task)
We should make sure that no value-tuples are returned and that they are not in the parameters of any public API.
Related to: #2487