Find a way to speed up server status building

The builder class to create router statuses is taking more than 24h to run. We are loosing data as a result.

This is probably due to having to query different tables in the DB to build the status records.

There are a number of steps that could be done to take a few queries less. One of these steps is adding the first network status digest to router status table, so that we don't have to query all the statuses for that router and select the first one by time.

This ticket should track these optimization strategies and implement them in the code.