Split off from #34850 by Guido's request.

To help catch incorrect use of `is` when `==` is intended, perhaps we should add an interpreter mode that disables the caches for small ints and interned strings.

Nathaniel called it "chaos mode" but I don't like the name as there is nothing chaotic about the lack of such caches, and it doesn't come close to chaos testing (e.g. Netflix's Chaos Monkey tool).