Investigate client-side validations of data coming from a beacon node to the validator client

There are some simple sanity-check type validations we can do when we get data from a beacon node as the validator client.

The extent to which we want to validate the data depends on our trust model, where we already trust the beacon node to great extent. This being said we could still check the data we get back is the data we expect, more to account for programmer error than malicious behavior.