Various DeprecationWarnings and others have crept up.

• datetime.utcnow() (naive) -> datetime.now(UTC) (localized), and any comparisons with the result of this also need to be localized
• sparse.COO wants true numpy arrays, not Python lists.
• pandas removed delim_whitespace.
• TemplateResponse changed around its signature.
• FileResponse no longer accepts method parameter (it's implicitly always GET).

Checklist

• Add a Changelog entry
• Add the ticket number which this PR closes to the comment section