Rust iterator impl

Every error text, warning, and number below comes from rustc 1.98.1, edition 2024, on aarch64-apple-darwin.

Route the symptom to a section

Symptom or task	Section
`error[E0277]: &Bag is not an iterator` on `for v in &bag`	The three IntoIterator impls
`error[E0658]: impl Trait in associated types is unstable` on `type IntoIter`	The three IntoIterator impls
`warning: function cannot return without recursing`, then `has overflowed its stack`	Never call self.into_iter() in the impl
`error[E0277]: a value of type X cannot be built from an iterator`	A collection newtype needs four impls
`error[E0207]: the lifetime parameter 'a is not constrained`	Iterator cannot borrow from itself
A panic inside `core/src/iter/traits/exact_size.rs`	size_hint is a contract
`error[E0277]: ... ExactSizeIterator is not satisfied`, pointing at `.rev()`	Adapter order
`error[E0658]: gen blocks are experimental`	Stateful generators
`error[E0432]: unresolved import std::ops::Generator`	Stateful generators
The impls are correct, and iteration is slow	the `rust-hot-path` skill