Chore: Queued event system (#5514)

* implemented queued event system

* implemented basic tests

tests/unit/openpype/lib/test_event_system.py

@@ -0,0 +1,83 @@
+from openpype.lib.events import EventSystem, QueuedEventSystem
+
+
+def test_default_event_system():
+    output = []
+    expected_output = [3, 2, 1]
+    event_system = EventSystem()
+
+    def callback_1():
+        event_system.emit("topic.2", {}, None)
+        output.append(1)
+
+    def callback_2():
+        event_system.emit("topic.3", {}, None)
+        output.append(2)
+
+    def callback_3():
+        output.append(3)
+
+    event_system.add_callback("topic.1", callback_1)
+    event_system.add_callback("topic.2", callback_2)
+    event_system.add_callback("topic.3", callback_3)
+
+    event_system.emit("topic.1", {}, None)
+
+    assert output == expected_output, (
+        "Callbacks were not called in correct order")
+
+
+def test_base_event_system_queue():
+    output = []
+    expected_output = [1, 2, 3]
+    event_system = QueuedEventSystem()
+
+    def callback_1():
+        event_system.emit("topic.2", {}, None)
+        output.append(1)
+
+    def callback_2():
+        event_system.emit("topic.3", {}, None)
+        output.append(2)
+
+    def callback_3():
+        output.append(3)
+
+    event_system.add_callback("topic.1", callback_1)
+    event_system.add_callback("topic.2", callback_2)
+    event_system.add_callback("topic.3", callback_3)
+
+    event_system.emit("topic.1", {}, None)
+
+    assert output == expected_output, (
+        "Callbacks were not called in correct order")
+
+
+def test_manual_event_system_queue():
+    output = []
+    expected_output = [1, 2, 3]
+    event_system = QueuedEventSystem(auto_execute=False)
+
+    def callback_1():
+        event_system.emit("topic.2", {}, None)
+        output.append(1)
+
+    def callback_2():
+        event_system.emit("topic.3", {}, None)
+        output.append(2)
+
+    def callback_3():
+        output.append(3)
+
+    event_system.add_callback("topic.1", callback_1)
+    event_system.add_callback("topic.2", callback_2)
+    event_system.add_callback("topic.3", callback_3)
+
+    event_system.emit("topic.1", {}, None)
+
+    while True:
+        if event_system.process_next_event() is None:
+            break
+
+    assert output == expected_output, (
+        "Callbacks were not called in correct order")