In this commit, we modify our TxConfNotifier struct to allow handling
notification registrations asynchronously. The Register method has been
refactored into two: Register and UpdateConfDetails. In the case that a
transaction we registered for notifications on has already confirmed,
we'll need to determine its confirmation details on our own. Once done,
this can be provided within UpdateConfDetails.
This change will pave down the road for our different chain notifiers to
handle potentially long rescans asynchronously to prevent blocking the
caller.
In this commit, we introduce the ability for the different ChainNotifier
implements to send incremental updates to the subscribers of transaction
confirmations. These incremental updates represent how many
confirmations are left for the transaction to be confirmed. They are
sent to the subscriber at every new height of the chain.
In this commit, we add a new Updates channel to our ConfirmationEvent
struct. This channel will be used to deliver updates to a subscriber of
a confirmation notification. Updates will be delivered at every
incremental height of the chain with the number of confirmations
remaining for the transaction to be considered confirmed by the
subscriber.
