synchronizer: request missing txs for addresses in random order

as discussed in issue #6697, users with large wallets or slow
connections may never see their initial request-missing-tx run complete,
if we always use the same sync order.

This commit shuffles the addresses being requested every time a new
request round happens, so that (if enough time passes and enough initial
state requests are attempted) we will always get the latest state for
each address, regardless of how quickly the connection times out on us

electrum/synchronizer.py

@@ -232,7 +232,7 @@ class Synchronizer(SynchronizerBase):
     async def main(self):
         self.wallet.set_up_to_date(False)
         # request missing txns, if any
-        for addr in self.wallet.db.get_history():
+        for addr in random_shuffled_copy(self.wallet.db.get_history()):
             history = self.wallet.db.get_addr_history(addr)
             # Old electrum servers returned ['*'] when all history for the address
             # was pruned. This no longer happens but may remain in old wallets.