Clippy pre beta branch fix Before beta is branched on Friday, I want to move the `unused_peekable` lint that was added in this release cycle (1.65) to `nursery`. This lint was already reported twice (https://github.com/rust-lang/rust-clippy/issues/9456, https://github.com/rust-lang/rust-clippy/issues/9462) in a short time, so it is probably a good idea to fix it before it hits beta and then stable. r? `@Manishearth`