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_flags/test_decorator.py

@@ -0,0 +1,66 @@
+import pytest
+
+from aiogram.dispatcher.flags import Flag, FlagDecorator, FlagGenerator
+
+
+@pytest.fixture(name="flag")
+def flag_fixture() -> Flag:
+    return Flag("test", True)
+
+
+@pytest.fixture(name="flag_decorator")
+def flag_decorator_fixture(flag: Flag) -> FlagDecorator:
+    return FlagDecorator(flag)
+
+
+@pytest.fixture(name="flag_generator")
+def flag_flag_generator() -> FlagGenerator:
+    return FlagGenerator()
+
+
+class TestFlagDecorator:
+    def test_with_value(self, flag_decorator: FlagDecorator):
+        new_decorator = flag_decorator._with_value(True)
+
+        assert new_decorator is not flag_decorator
+        assert new_decorator.flag is not flag_decorator.flag
+        assert new_decorator.flag
+
+    def test_call_invalid(self, flag_decorator: FlagDecorator):
+        with pytest.raises(ValueError):
+            flag_decorator(True, test=True)
+
+    def test_call_with_function(self, flag_decorator: FlagDecorator):
+        def func():
+            pass
+
+        decorated = flag_decorator(func)
+        assert decorated is func
+        assert hasattr(decorated, "aiogram_flag")
+
+    def test_call_with_arg(self, flag_decorator: FlagDecorator):
+        new_decorator = flag_decorator("hello")
+        assert new_decorator is not flag_decorator
+        assert new_decorator.flag.value == "hello"
+
+    def test_call_with_kwargs(self, flag_decorator: FlagDecorator):
+        new_decorator = flag_decorator(test=True)
+        assert new_decorator is not flag_decorator
+        assert isinstance(new_decorator.flag.value, dict)
+        assert "test" in new_decorator.flag.value
+
+
+class TestFlagGenerator:
+    def test_getattr(self):
+        generator = FlagGenerator()
+        assert isinstance(generator.foo, FlagDecorator)
+        assert isinstance(generator.bar, FlagDecorator)
+
+        assert generator.foo is not generator.foo
+        assert generator.foo is not generator.bar
+
+    def test_failed_getattr(self):
+        generator = FlagGenerator()
+
+        with pytest.raises(AttributeError):
+            generator._something