Add pubsub event system and integrate sync notifications

src/tests/test_pubsub.py

@@ -0,0 +1,28 @@
+from seedpass.core.pubsub import PubSub
+
+
+def test_subscribe_and_publish():
+    bus = PubSub()
+    calls = []
+
+    def handler(arg):
+        calls.append(arg)
+
+    bus.subscribe("event", handler)
+    bus.publish("event", 123)
+
+    assert calls == [123]
+
+
+def test_unsubscribe():
+    bus = PubSub()
+    calls = []
+
+    def handler():
+        calls.append(True)
+
+    bus.subscribe("event", handler)
+    bus.unsubscribe("event", handler)
+    bus.publish("event")
+
+    assert calls == []