add to_numpy methods

[basnijholt]

Description

After having answered "How do I get the data" 1000 times and having written the code to convert learner.data to a numpy array many times as well, I decided to just add it in Adaptive.

I have implemented it such that a single array is returned with the points and values concatenated. An alternative is to return the points and values as separate arrays.

Checklist

• Fixed style issues using pre-commit run --all (first install using pip install pre-commit)
• pytest passed

Type of change

Check relevant option(s).

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• (Code) style fix or documentation update
• This change requires a documentation update

[jbweston]

LGTM. Should we also add this to the documentation?

[basnijholt]

Should be in the API docs :-)

Thanks for merging!