This PR moves the sweeper logic from
A follow up PR is #2000, which will let resolvers use the sweeper directly instead of going through nursery. The end goal is to remove nursery completely.
In this PR, there is no db migration to clean up now unused nursery store data. This allows us to keep the downgrade path open for a while.
Modifying the static fees is not thread safe. In this commit the fees are made immutable.
This commit is a preparation for the implementation of remote spend detection. Remote spends may happen before we broadcast our own sweep tx. This calls for accurate height hints.
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.