Move imports in mqtt component (#27835)

* move imports to top-level in mqtt server

* move imports to top-level in mqtt configflow

* move imports to top-level in mqtt init

* move imports to top-level in mqtt vacuum

* move imports to top-level in mqtt light

homeassistant/components/mqtt/models.py

@@ -0,0 +1,20 @@
+"""Modesl used by multiple MQTT modules."""
+from typing import Union, Callable
+
+import attr
+
+# pylint: disable=invalid-name
+PublishPayloadType = Union[str, bytes, int, float, None]
+
+
+@attr.s(slots=True, frozen=True)
+class Message:
+    """MQTT Message."""
+
+    topic = attr.ib(type=str)
+    payload = attr.ib(type=PublishPayloadType)
+    qos = attr.ib(type=int)
+    retain = attr.ib(type=bool)
+
+
+MessageCallbackType = Callable[[Message], None]