Rust 1.83, allow -> expect (missing_docs)

[bas-ie]

Objective

We were waiting for 1.83 to address most of these, due to a bug with missing_docs and expect. Relates to, but does not entirely complete, #15059.

Solution

• Upgrade to 1.83
• Switch allow(missing_docs) to expect(missing_docs)
• Remove a few now-unused allows along the way, or convert to expect

[bas-ie]

Let's see what the CI has to say now :eyes:

[BenjaminBrienen]

I think you can use expect there if you use cfg_attr.