In this commit, we extend the NeutrinoNotifier to support registering
scripts for spends notifications. Once the script has been detected as
spent within the chain, a spend notification will be dispatched through
the Spend channel of the SpendEvent returned upon registration.
For scripts that have been spent in the past, the rescan logic has been
modified to match on the script rather than the outpoint. A concurrent
queue for relevant transactions has been added to proxy notifications
from the underlying rescan to the txNotifier. This is needed for
scripts, as we cannot perform a historical rescan for scripts through
`GetUtxo`, like we do with outpoints.
For scripts that are unspent, a filter update is sent to the underlying
rescan to ensure that we match and dispatch on the script when
processing new blocks.
Along the way, we also address an issue where we'd miss detecting that
an outpoint/script has been spent in the future due to not receiving a
historical dispatch request from the underlying txNotifier. To fix this,
we ensure that we always request the backend to notify us of the spend
once it detects it at tip, regardless of whether a historical rescan was
detected or not.
In this commit, we modify the logic within RegisterSpendNtfn for the
NeutrinoNotifier to account for the recent changes made to the
TxNotifier. Since it is now able to handle spend notification
registration and dispatch, we can bypass all the current logic within
the NeutrinoNotifier and interact directly with the TxNotifier instead.
The most notable change is that now we'll only attempt a historical
rescan if the TxNotifier tells us so.
