Verify randomness returned by drand REST API

[bajtos]

We had to disable DRAND beacon verification because it did not work when using drand-client via CDN. Without the verification, we are blindly trusting https://api.drand.sh/ to provide honest responses.

Let's fix that.

Options to consider:

• Find a CDN that can correctly bundle drand-client and all of its dependencies.
• Replace drand-client with our own implementation and implement the beacon verification algorithm using Web Crypto instead of @subtle/hash.