Dev 3.x flat package (#961)

* Move packages

* Added changelog

* Update examples/echo_bot.py

Co-authored-by: Oleg A. <t0rr@mail.ru>

* Rename `handler` -> `handlers`

* Update __init__.py

Co-authored-by: Oleg A. <t0rr@mail.ru>

tests/test_handler/test_callback_query.py

@@ -0,0 +1,28 @@
+from typing import Any
+
+import pytest
+
+from aiogram.handlers import CallbackQueryHandler
+from aiogram.types import CallbackQuery, User
+
+pytestmark = pytest.mark.asyncio
+
+
+class TestCallbackQueryHandler:
+    async def test_attributes_aliases(self):
+        event = CallbackQuery(
+            id="chosen",
+            from_user=User(id=42, is_bot=False, first_name="Test"),
+            data="test",
+            chat_instance="test",
+        )
+
+        class MyHandler(CallbackQueryHandler):
+            async def handle(self) -> Any:
+                assert self.event == event
+                assert self.from_user == self.event.from_user
+                assert self.callback_data == self.event.data
+                assert self.message == self.message
+                return True
+
+        assert await MyHandler(event)