Add (partial) train+eval model template nb

[bdewilde]

changes

• adds a partial model training+evaluation template notebook for pdp schools, with TODOs marked for where future work is needed
• fixes a bug in a modeling util function

context

Trying to extend the template school-agnostic pipeline further, from end to end.

questions

Any objections to committing this in partial form, for future dev work?

[nm3224]

all good!

[bdewilde]

Hey @nm3224 , thanks for taking a look, but just want to clarify expectations / process around PRs:

• if you're not tagged as a reviewer (or haven't otherwise been requested), don't feel any obligation to review! in fact, it's probably better to leave it to the reviewers, since they may have context that you don't have.
• when submitting reviews, please leave the actual merging (or closing) of the PR to the person who submitted it. there may be dependencies between PRs or other cleanup work that they need to take care of first.
• finally, "closing" a PR doesn't merge, it just sends the code you've reviewed into the dustbin of history.