AddressSynchronizer.add_address called synchronizer.add, which would only
schedule adding the addr to the Synchronizer in the next event loop iter.
If during that time, the synchronizer called adb.set_up_to_date(True),
the wallet would falsely believe and advertise itself as up_to_date
(as the wallet would see wallet.synchronize not creating new addresses,
and adb (via synchronizer) telling it is up_to_date).
Moments later, the synchronizer._add_address is finally executed and
up_to_date=False propagates out synchronizer->adb->wallet.
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