fix: remove updater blocktime x finality latency between updates

[luketchang]

Problem

• Currently, updater must wait till its last update becomes final to move onto producing a new one (does so by re-reading its own update on a timelag)
• This incurs a blocktime x finality latency for between each update
• If you dispatch a message that reaches finality just after the last update was submitted, you have a potentially 2 x (blocktime x finality) latency

Solution

• We know that the all updates produced in db will be valid chain, thus the new_root of the prev produced update will always be the old_root of the next produced update
• UpdateProducer should immediately retrieve next root to build off of from produced updates db