Deprecations in forthcoming dependency upgrade

[EliahKagan]

Based on testing in my fork (such as in EliahKagan#46), a forthcoming Dependabot PR will introduce dependencies that fail linting due to two deprecations, and which I plan to fix by cherry-picking two commits from a branch in my fork where I have already tested them:

• tempfile 3.20.0 introduces TempDir::keep(), deprecating the name TempDir::into_path() (67691ee).
• criterion 0.6.0 deprecates criterion::black_box(), recommending std::hint::black_box() (2e75ff3).

The purpose of this issue is just to document that I have these changes ready, to avert duplication of work. (The alternative of manually triggering an early Dependabot scan, or otherwise applying the updates, would have the drawback that Dependabot would then still open the scheduled PR if any update became available in between, increasing churn.)

[Byron]

It's amazing that you set everything up to be able to pre-empt these upgrades even, it's truly amazing work 🙇.