Upgrade to twox-hash 2.0

[shepmaster]

Thanks for using my crate!

Note that version 2.0 increases the MSRV to Rust 1.81. I understand if you don't want to upgrade right away, but hopefully this PR will be useful when you do.

I'm opening these PRs for the top users of twox-hash and have no current plans to become a consistent contributor to this specific repository; please feel free to rewrite the commit as appropriate for your project's requirements.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[Manishearth]

Superseded by #5709 so you don't have to deal with the CLA.

[shepmaster]

Thanks!