Validated number questions in multipart type

[alexgoff]

What this change does

Add validated numbers to multipart questions and do some cleanup and extraction of multipart questions

Notes for reviewers

Client + API changes

Testing

• Create a multipart question in Craft, add a number with validations
• Observe on the page that validations work as intended (additionally check a standalone number question to see that it also still works)
• Observe that the question also displays in the review page and in XLSX

Resolves #171

[github-actions]

A preview of this PR will be available at https://agmultipartvalidations-dot-investigations-client-dot-skyviewer.uw.r.appspot.com until the request is closed.