Previously, nursery generated and published its own sweep txes. It
stored the sweep tx in nursery_store to prevent a new tx with a new
sweep address from being generated on restart.
In this commit, sweep generation and publication is removed from nursery
and delegated to the sweeper. Also the confirmation notification is
received from the sweeper.
In this commit, we aim to address a lingering bug caused by a Late
Registration of a kid output from preschool to kindergarten. In this
scenario, an output is promoted, but *after* it’s target maturity
period, meaning that we won’t graduate the output until we restart. To
avoid this, we’ll now detect this case, and bump the graduation height
by one to ensure that when the new block arrives, we properly handle
the output.
