type hints: (trivial) small fixes all over

### electrum/gui/qml/qetxfinalizer.py
@@ -941,7 +941,7 @@ def __init__(self, parent=None):
         self._parent_tx = None
         self._new_tx = None
         self._parent_tx_size = 0
-        self._parent_fee = 0
+        self._parent_fee = 0  # type: int | None
         self._max_fee = 0
         self._txid = ''
         self._rbf = True

### electrum/gui/qt/main_window.py
@@ -184,7 +184,7 @@ def __init__(self, gui_object: 'ElectrumGui', wallet: Abstract_Wallet):
 
         Exception_Hook.maybe_setup(config=self.config, wallet=self.wallet)
 
-        self.network = gui_object.daemon.network  # type: Network
+        self.network = gui_object.daemon.network  # type: Network | None
         self.fx = gui_object.daemon.fx  # type: FxThread
         self.contacts = wallet.contacts
         self.tray = gui_object.tray

### electrum/invoices.py
@@ -257,7 +257,7 @@ def as_dict(self, status):
 @attr.s
 class Invoice(BaseInvoice):
     lightning_invoice = attr.ib(type=str, kw_only=True)  # type: Optional[str]
-    __lnaddr = None
+    __lnaddr = None  # type: BOLT11Addr | None
     _broadcasting_status = None # can be None or PR_BROADCASTING or PR_BROADCAST
 
     def is_lightning(self):

### electrum/lnonion.py
@@ -389,7 +389,7 @@ class ProcessedOnionPacket(NamedTuple):
     are_we_final: bool
     hop_data: OnionHopsDataSingle
     next_packet: OnionPacket
-    trampoline_onion_packet: OnionPacket
+    trampoline_onion_packet: OnionPacket | None
 
     @property
     def amt_to_forward(self) -> Optional[int]:

### electrum/plugins/watchtower/watchtower.py
@@ -152,7 +152,7 @@ async def check_onchain_situation(self, address, funding_outpoint):
         if not keep_watching:
             await self.unwatch_channel(address, funding_outpoint)
 
-    def inspect_tx_candidate(self, outpoint, n: int) -> Dict[str, str]:
+    def inspect_tx_candidate(self, outpoint: str, n: int) -> Dict[str, str | None]:
         """
         returns a dict of spenders for a transaction of interest.
         subscribes to addresses as a side effect.

### electrum/submarine_swaps.py
@@ -253,11 +253,11 @@ class SwapManager(Logger):
 
     def __init__(self, *, wallet: 'Abstract_Wallet', lnworker: 'LNWallet'):
         Logger.__init__(self)
-        self.mining_fee = None
+        self.mining_fee = None  # type: int | None
         self.percentage = None  # type: Optional[Decimal]
-        self._min_amount = None
-        self._max_forward = None
-        self._max_reverse = None
+        self._min_amount = None  # type: int | None
+        self._max_forward = None  # type: int | None
+        self._max_reverse = None  # type: int | None
 
         self.wallet = wallet
         self.config = wallet.config

### electrum/transaction.py
@@ -907,8 +907,8 @@ def __init__(self, raw):
             self._cached_network_ser = raw.hex()
         else:
             raise Exception(f"cannot initialize transaction from {raw}")
-        self._inputs = None  # type: List[TxInput]
-        self._outputs = None  # type: List[TxOutput]
+        self._inputs = None  # type: List[TxInput] | None
+        self._outputs = None  # type: List[TxOutput] | None
         self._locktime = 0
         self._version = 2
 
@@ -2495,7 +2495,7 @@ def sign_txin(
         txin_index: int,
         privkey_bytes: bytes,
         *,
-        sighash_cache: SighashCache = None,
+        sighash_cache: SighashCache | None = None,
     ) -> bytes:
         txin = self.inputs()[txin_index]
         txin.validate_data(for_signing=True)

### tests/test_commands.py
@@ -748,7 +748,7 @@ async def test_add_peer(self, *mock_args):
         mock_peer = mock.Mock()
         mock_peer.initialized = asyncio.Future()
         connection_string = "test_node_id@127.0.0.1:9735"
-        called = False
+        called = 0
         async def lnpeermgr_add_peer(*args, **kwargs):
             assert args[0] == connection_string
             nonlocal called

### tests/test_lnpeer.py
@@ -2668,7 +2668,7 @@ async def test_forwarder_fails_for_inconsistent_trampoline_onions(self):
         """
 
         # store a modified trampoline onion to be injected into lnworker.new_onion_packet later when sending the htlcs
-        modified_trampoline_onion = None
+        modified_trampoline_onion = None  # type: OnionPacket | None
         def modified_new_onion_packet_trampoline(payment_path_pubkeys, session_key, hops_data: List[OnionHopsDataSingle], **kwargs):
             nonlocal modified_trampoline_onion
             assert modified_trampoline_onion is None, "this mock should get called only once"

### tests/toyserver/toyserver.py
@@ -62,7 +62,7 @@ def recurse(node: str):
 @dataclass(kw_only=True, slots=True, frozen=True)
 class FakeBlock:
     header: bytes
-    txids: Sequence[str] = None  # FIXME needs OrderedSet with index-based lookup? >.<
+    txids: Sequence[str] | None = None  # FIXME needs OrderedSet with index-based lookup? >.<
 
     def __post_init__(self):
         if self.txids is None: