Improve assert_eq! and assert_ne! This PR improves `assert_eq!` and `assert_ne!` by moving the panicking code in an external function. It does not change the fast path, but the move of the formatting in the cold path (the panic) may have a positive effect on in instruction cache use and with inlining. Moreover, the use of trait objects instead of generic may improve compile times for `assert_eq!`-heavy code. Godbolt link: ~~https://rust.godbolt.org/z/TYa9MT~~ \ Updated: https://rust.godbolt.org/z/bzE84x