1. Since all of these callsites don't await on the Rust calls, we know we're not blocking execution and it doesn't really matter how early we call getRustAPI... delaying the Rust call for a couple seconds won't affect performance.
2. In siweAuthResponder, we were missing an await, which could lead to a "unhandled promise rejection" error from Node. D6944 has the same issue; if it's landed before this diff with that unaddressed, I'll update this diff to also address that.

I only tested this by running Flow... I feel fairly confident about the changes, but it would be good if we could test the whole identity service / keyserver flow end-to-end after this and the other outstanding diffs are landed