contacts: fix adding new contacts

This is a regression from 7ca89f56ee, which introduced StoredList.
The newly added test was failing without the change.

```
Traceback (most recent call last):
  File "/home/user/wspace/electrum/electrum/gui/qt/main_window.py", line 1786, in new_contact_dialog
    self.set_contact(line2.text(), line1.text())
  File "/home/user/wspace/electrum/electrum/gui/qt/main_window.py", line 1435, in set_contact
    self.contacts[address] = ('address', label)
  File "/home/user/wspace/electrum/electrum/contacts.py", line 75, in __setitem__
    self.save()
  File "/home/user/wspace/electrum/electrum/contacts.py", line 62, in save
    self.db.put('contacts', dict(self))
  File "/home/user/wspace/electrum/electrum/json_db.py", line 42, in wrapper
    return func(self, *args, **kwargs)
  File "/home/user/wspace/electrum/electrum/json_db.py", line 318, in put
    self.data[key] = copy.deepcopy(value)
  File "/usr/lib/python3.10/copy.py", line 146, in deepcopy
    y = copier(x, memo)
  File "/usr/lib/python3.10/copy.py", line 231, in _deepcopy_dict
    y[deepcopy(key, memo)] = deepcopy(value, memo)
  File "/usr/lib/python3.10/copy.py", line 172, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "/usr/lib/python3.10/copy.py", line 271, in _reconstruct
    state = deepcopy(state, memo)
  File "/usr/lib/python3.10/copy.py", line 146, in deepcopy
    y = copier(x, memo)
  File "/usr/lib/python3.10/copy.py", line 231, in _deepcopy_dict
    y[deepcopy(key, memo)] = deepcopy(value, memo)
  File "/usr/lib/python3.10/copy.py", line 172, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "/usr/lib/python3.10/copy.py", line 271, in _reconstruct
    state = deepcopy(state, memo)
  File "/usr/lib/python3.10/copy.py", line 146, in deepcopy
    y = copier(x, memo)
  File "/usr/lib/python3.10/copy.py", line 231, in _deepcopy_dict
    y[deepcopy(key, memo)] = deepcopy(value, memo)
  File "/usr/lib/python3.10/copy.py", line 161, in deepcopy
    rv = reductor(4)
TypeError: cannot pickle '_thread.RLock' object
```

electrum/tests/test_contacts.py

@@ -0,0 +1,31 @@
+import os
+
+from . import ElectrumTestCase
+
+from electrum.simple_config import SimpleConfig
+from electrum.wallet import restore_wallet_from_text, Abstract_Wallet
+from electrum.daemon import Daemon
+
+
+class TestContacts(ElectrumTestCase):
+    TESTNET = True
+
+    def setUp(self):
+        super().setUp()
+        self.config = SimpleConfig({'electrum_path': self.electrum_path})
+        self.wallet_path = os.path.join(self.electrum_path, "somewallet1")
+
+    async def test_saving_contacts(self):
+        text = 'cross end slow expose giraffe fuel track awake turtle capital ranch pulp'
+        d = restore_wallet_from_text(text, path=self.wallet_path, gap_limit=2, config=self.config)
+        w = d['wallet']  # type: Abstract_Wallet
+        w.contacts["myNNuLYNgHE92nGQuJd5mXo6gy9gKXEDyQ"] = ("address", "alice")
+        w.contacts["tb1q4syjltptqwhe62t3u5gwz9nsw87kmcwx003z05"] = ("address", "bob")
+        self.assertEqual(2, len(w.contacts))
+        await w.stop()
+        del w
+        # re-open wallet from disk
+        w = Daemon._load_wallet(self.wallet_path, password=None, config=self.config)
+        self.assertEqual(2, len(w.contacts))
+        w.contacts["n4STqqWPrvkapAyvXY2wJzfoKMnuJbDWoH"] = ("address", "carol")
+        self.assertEqual(3, len(w.contacts))

electrum/wallet_db.py

@@ -103,6 +103,7 @@ class WalletFileExceptionVersion51(WalletFileException): pass
 json_db.register_dict('transactions', lambda x: tx_from_any(x, deserialize=False), None)
 json_db.register_dict('prevouts_by_scripthash', lambda x: set(tuple(k) for k in x), None)
 json_db.register_dict('data_loss_protect_remote_pcp', lambda x: bytes.fromhex(x), None)
+json_db.register_dict('contacts', tuple, None)
 # register dicts that require key conversion
 for key in [
         'adds', 'locked_in', 'settles', 'fails', 'fee_updates', 'buckets',