hw wallets: introduce HardwareHandlerBase

previously, client.handler was sometimes
- an InstallWizard
- a QtHandlerBase where win was an ElectrumWindow
- a QtHandlerBase where win was an InstallWizard
- a CmdLineHandler

That's just too much dynamic untyped undocumented polymorphism...
Now it will never be an InstallWizard (replaced with QtHandlerBase where win is an InstallWizard),
and now in all cases client.handler is an instance of HardwareHandlerBase, yay.

related: #6063

electrum/plugin.py

@@ -39,7 +39,7 @@ from .simple_config import SimpleConfig
 from .logging import get_logger, Logger
 
 if TYPE_CHECKING:
-    from .plugins.hw_wallet import HW_PluginBase, HardwareClientBase
+    from .plugins.hw_wallet import HW_PluginBase, HardwareClientBase, HardwareHandlerBase
     from .keystore import Hardware_KeyStore
 
 
@@ -386,7 +386,8 @@ class DeviceMgr(ThreadJob):
     def register_enumerate_func(self, func):
         self.enumerate_func.add(func)
 
-    def create_client(self, device: 'Device', handler, plugin: 'HW_PluginBase') -> Optional['HardwareClientBase']:
+    def create_client(self, device: 'Device', handler: Optional['HardwareHandlerBase'],
+                      plugin: 'HW_PluginBase') -> Optional['HardwareClientBase']:
         # Get from cache first
         client = self.client_lookup(device.id_)
         if client:
@@ -447,7 +448,8 @@ class DeviceMgr(ThreadJob):
         self.scan_devices()
         return self.client_lookup(id_)
 
-    def client_for_keystore(self, plugin: 'HW_PluginBase', handler, keystore: 'Hardware_KeyStore',
+    def client_for_keystore(self, plugin: 'HW_PluginBase', handler: Optional['HardwareHandlerBase'],
+                            keystore: 'Hardware_KeyStore',
                             force_pair: bool) -> Optional['HardwareClientBase']:
         self.logger.info("getting client for keystore")
         if handler is None:
@@ -468,7 +470,7 @@ class DeviceMgr(ThreadJob):
         self.logger.info("end client for keystore")
         return client
 
-    def client_by_xpub(self, plugin: 'HW_PluginBase', xpub, handler,
+    def client_by_xpub(self, plugin: 'HW_PluginBase', xpub, handler: 'HardwareHandlerBase',
                        devices: Iterable['Device']) -> Optional['HardwareClientBase']:
         _id = self.xpub_id(xpub)
         client = self.client_lookup(_id)
@@ -482,7 +484,7 @@ class DeviceMgr(ThreadJob):
             if device.id_ == _id:
                 return self.create_client(device, handler, plugin)
 
-    def force_pair_xpub(self, plugin: 'HW_PluginBase', handler,
+    def force_pair_xpub(self, plugin: 'HW_PluginBase', handler: 'HardwareHandlerBase',
                         info: 'DeviceInfo', xpub, derivation) -> Optional['HardwareClientBase']:
         # The wallet has not been previously paired, so let the user
         # choose an unpaired device and compare its first address.
@@ -510,7 +512,8 @@ class DeviceMgr(ThreadJob):
               'its seed (and passphrase, if any).  Otherwise all bitcoins you '
               'receive will be unspendable.').format(plugin.device))
 
-    def unpaired_device_infos(self, handler, plugin: 'HW_PluginBase', devices: List['Device'] = None,
+    def unpaired_device_infos(self, handler: Optional['HardwareHandlerBase'], plugin: 'HW_PluginBase',
+                              devices: List['Device'] = None,
                               include_failing_clients=False) -> List['DeviceInfo']:
         '''Returns a list of DeviceInfo objects: one for each connected,
         unpaired device accepted by the plugin.'''
@@ -539,7 +542,7 @@ class DeviceMgr(ThreadJob):
 
         return infos
 
-    def select_device(self, plugin: 'HW_PluginBase', handler,
+    def select_device(self, plugin: 'HW_PluginBase', handler: 'HardwareHandlerBase',
                       keystore: 'Hardware_KeyStore', devices: List['Device'] = None) -> 'DeviceInfo':
         '''Ask the user to select a device to use if there is more than one,
         and return the DeviceInfo for the device.'''
@@ -581,8 +584,9 @@ class DeviceMgr(ThreadJob):
         info = infos[c]
         # save new label
         keystore.set_label(info.label)
-        if handler.win.wallet is not None:
-            handler.win.wallet.save_keystore()
+        wallet = handler.get_wallet()
+        if wallet is not None:
+            wallet.save_keystore()
         return info
 
     def _scan_devices_with_hid(self) -> List['Device']: