Add pagination to the `CheckNullifiersByPrefix` endpoint

[bobbinth]

We should make sure that CheckNullifiersByPrefix never turns too much data in a single response. For this, we can use a similar strategy as we did with SyncStorageMaps and SyncAccountVault endpoints. Specifically:

We can impose a limit on the number of nullifiers returned from the database, and if the returned number of records is greater than or equal to this limit, we discard the last block of data. The user then will have to make a new request with the last returned block number + 1.

As with other two responses, we should try to limit the response size to ~ 2MB - though, at some point, we should make this a configurable setting.