Feature request: a debug-only version of `zip_eq`

[BugenZhao]

As it's known that zip_eq kills the performance, but I appreciate that it has helped to find a lot of runtime issues. So I'm curious whether it's worthwhile to add a debug-only version of zip_eq which directly forwards the implementation to std::iter::Zip when debug_assertions is off? We may let it return an opaque type to achieve this.