Blockchain's notificationDispatcher sends events to channels and these
channels must be read from. Unfortunately, regular service shutdown procedure
does unsubscription first (outside of the read loop) and only then drains the
channel. While it waits for unsubscription request to be accepted
notificationDispatcher can try pushing more data into the same channel which
will lead to a deadlock. Reading in the same method solves this, any number of
events can be pushed until unsub channel accepts the data.
Which allows to enable/disable the service, change nodes, keys and other
settings. Unfortunately, atomic.Value doesn't allow Store(nil), so we have to
store a pointer there that can point to nil interface.
It's not an ideal solution, but at least it solves the problem for
now. Caveats:
* consensus only needs one method, so it's mirrored to Blockchain
* rpcsrv uses core.* definition of the StateRoot (so technically it might as
well not have an internal Ledger), but it uses core already unfortunately
1. It's not good for pkg/core to import anything from pkg/neorpc.
2. The type is closely tied to the state package, even though it's not stored
in the DB
