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_shipping_query.py

@@ -0,0 +1,33 @@
+from typing import Any
+
+import pytest
+
+from aiogram.handlers import ShippingQueryHandler
+from aiogram.types import ShippingAddress, ShippingQuery, User
+
+pytestmark = pytest.mark.asyncio
+
+
+class TestShippingQueryHandler:
+    async def test_attributes_aliases(self):
+        event = ShippingQuery(
+            id="query",
+            from_user=User(id=42, is_bot=False, first_name="Test"),
+            invoice_payload="payload",
+            shipping_address=ShippingAddress(
+                country_code="country_code",
+                state="state",
+                city="city",
+                street_line1="street_line1",
+                street_line2="street_line2",
+                post_code="post_code",
+            ),
+        )
+
+        class MyHandler(ShippingQueryHandler):
+            async def handle(self) -> Any:
+                assert self.event == event
+                assert self.from_user == self.event.from_user
+                return True
+
+        assert await MyHandler(event)