Audit default clippy lints

Some clippy lints are helpful for libraries, but not on by default. For example `exhaustive_struct` or `exhaustive_enum`.

For these lints it is often better to enable them workspace wide, and add `#[allow(...)]` to types that don't need it.

The full list of clippy lints is here: https://rust-lang.github.io/rust-clippy/master/index.html

That is too many to read. I asked Gemini to pick out the ones relevant to public libraries, like ours. Googlers can see the list it came up with: https://paste.googleplex.com/5402513244291072