network: randomise the order of address subscriptions

Before this, we were subscribing to our addresses in their bip32 order,
leaking this information to servers. While this leak seems mostly harmless,
it is trivial to fix.

electrum/util.py

@@ -24,7 +24,7 @@ import binascii
 import os, sys, re, json
 from collections import defaultdict, OrderedDict
 from typing import (NamedTuple, Union, TYPE_CHECKING, Tuple, Optional, Callable, Any,
-                    Sequence, Dict, Generic, TypeVar)
+                    Sequence, Dict, Generic, TypeVar, List, Iterable)
 from datetime import datetime
 import decimal
 from decimal import Decimal
@@ -1398,3 +1398,12 @@ class JsonRPCClient:
         async def coro(*args):
             return await self.request(endpoint, *args)
         setattr(self, endpoint, coro)
+
+
+T = TypeVar('T')
+
+def random_shuffled_copy(x: Iterable[T]) -> List[T]:
+    """Returns a shuffled copy of the input."""
+    x_copy = list(x)  # copy
+    random.shuffle(x_copy)  # shuffle in-place
+    return x_copy