Close the database and free resources.
Retrieve posterior state of given header.
Compute a state root for given state.
Insert a full state into the database.
Apply & commit a state update.
NOTE: for efficiency, the implementation MAY alter given state object.
Interface for accessing states stored in the database.
NOTE that the design of this interface is heavily influenced by the LMDB implementation, so that we can implement it efficiently.
See the documentation there for more detailed reasoning.