- arrayvec.rs: Use concrete return types ([T], slice::Iter, slice::IterMut)
instead of Self::Target/Self::IntoIter to avoid E0223 ambiguity
introduced by the Receiver trait in Rust 1.87+
- char.rs: Explicitly import Result/Ok/Err from core for target_os=none
where the standard prelude is not auto-injected
