An agent that holds the current state of the Server/Slave DB.
@spec apply(atom() | pid() | {atom(), any()} | {:via, atom(), any()}, any()) :: any()
@spec start_link(any(), debug: [any()], hibernate_after: :infinity | non_neg_integer(), name: atom() | {any(), any()} | {any(), any(), any()}, spawn_opt: :link | :monitor | {any(), any()}, timeout: :infinity | non_neg_integer() ) :: {:error, any()} | {:ok, pid()}
@spec state(atom() | pid() | {atom(), any()} | {:via, atom(), any()}) :: any()
@spec stop(atom() | pid() | {atom(), any()} | {:via, atom(), any()}) :: :ok