Support nitriding v2?

[NullHypothesis]

With nitriding's tap support almost merged (see brave/nitriding#26), we now need to figure out how to move forward with the randomness server. I see two options:

1. Continue using the existing nitriding and do nothing (beyond fixing bugs). That's the simplest solution but it means that we are going to have to maintain nitriding in both v1 and v2, which is messy and a maintenance burden in the long term.
2. Re-implement the randomness server's front end in Rust, which gets rid of our foreign function interface. This means some work in the short term.

[NullHypothesis]

After a brief discussion on Slack, we agreed on option 2. Assigning this to @rillian for now.