helios-rot: make the trait / interface async

[flihp]

This is required to integrate an impl of HeliosRot into verifier-cli, and will be required for any future integration w/ sled-agent

[flihp]

CI failures don't look like they're caused by anything done in this PR: https://github.com/oxidecomputer/dice-util/actions/runs/34383199452/job/102572857725?pr=430#step:4:34. The internet says this is caused by a "network glitch" which I take to mean: just try again and hope github has sorted itself out ¯\_(ツ)_/¯

[flihp]

this is another instance of microsoft/linux-package-repositories#34 not actually being fixed

[flihp]

flipped this back to Draft while I poke at this

[flihp]

not related to microsoft/linux-package-repositories#34, instead it looks like actions/runner-images#7048 and / or actions/runner-images#12949. The summary from Microsoft in these issues is that the Ubuntu mirrors that they host in azure are unstable and shouldn't be used. They give instructions for disabling them in the linked issues which I'll give a shot here.