Cleanup credentials handling (#605)

* credentials: don't allow none to simplify checks

* Implement __bool__ for credentials

* Cleanup klaptransport cred usage

* Cleanup deviceconfig and tapodevice

* fix linting

* Pass dummy credentials for tests

* Remove __bool__ dunder and add docs to credentials

* Check for cred noneness in tapodevice.update()

kasa/tests/newfakes.py

@@ -305,7 +305,13 @@ class FakeSmartProtocol(SmartProtocol):
 class FakeSmartTransport(BaseTransport):
     def __init__(self, info):
         super().__init__(
-            config=DeviceConfig("127.0.0.123", credentials=Credentials()),
+            config=DeviceConfig(
+                "127.0.0.123",
+                credentials=Credentials(
+                    username="dummy_user",
+                    password="dummy_password",  # noqa: S106
+                ),
+            ),
         )
         self.info = info
 

kasa/tests/test_device_factory.py

@@ -76,7 +76,12 @@ async def test_connect_custom_port(all_fixture_data: dict, mocker, custom_port):
     host = "127.0.0.1"
 
     ctype, _ = _get_connection_type_device_class(all_fixture_data)
-    config = DeviceConfig(host=host, port_override=custom_port, connection_type=ctype)
+    config = DeviceConfig(
+        host=host,
+        port_override=custom_port,
+        connection_type=ctype,
+        credentials=Credentials("dummy_user", "dummy_password"),
+    )
     default_port = 80 if "discovery_result" in all_fixture_data else 9999
 
     ctype, _ = _get_connection_type_device_class(all_fixture_data)