Clippy nightly now gives a "missing panics doc" warning for expect()

This change seems to be the cause of our latest nightly fails: https://github.com/rust-lang/rust-clippy/pull/10953 .

There are around 54 affected functions in our codebase.

Before applying a fix here we should decide what we want to do about this change. Should we...

1. Stop caring about the missing_panics_doc warning?
2. See if we can get the clippy maintainers to split this into a separate lint?
3. Add either an allow(missing_panics_doc) annotation or a # Panics section to every function that calls expect()?

1 would be fastest, but I think 3 would not be totally out of line. I don't think our chances for 2 are great.