Investigate new Miri strict provenance flags

[jrvanwhy]

Miri has a new strict provenance flag, which we may want to enable: rust-lang/miri#2045

Open question: Is -Zmiri-strict-provenance strictly more restrictive than Miri's defaults (Stacked Borrows without -Zmiri-tag-raw-pointers)? If yes, perhaps we can deduplicate the Miri invocations to make make test faster?

[Gankra]

Yes it's strictly stricter, and implies -Zmiri-tag-raw-pointers too.

[jrvanwhy]

Yes it's strictly stricter, and implies -Zmiri-tag-raw-pointers too.

Fantastic, thank you for confirming!

[jrvanwhy]

-Zmiri-strict-provenance works fine for our unit tests. I'll send a PR once the toolchain update is merged.

@Gankra I have some questions about how strict provenance interacts with FFI. Where is the most appropriate place to ask them?