Fix state saving when sharing topics for MQTT entities (#79421)

* Do not write old state sharing availability topic

* Add a test

* Support for all availability topics

* delay async_write_ha_state till last callback

* Process write req after processing callback jobs

* Do not count subscription callbacks

* Simplify

* Stale docsting

* No topic needed for delays state write

* No need to clear when reloading

* Move test to test_mixins.py

* Only set up sensor platform for test

homeassistant/components/mqtt/siren.py

@@ -54,6 +54,7 @@ from .mixins import (
     warn_for_legacy_schema,
 )
 from .models import MqttCommandTemplate, MqttValueTemplate
+from .util import get_mqtt_data
 
 DEFAULT_NAME = "MQTT Siren"
 DEFAULT_PAYLOAD_ON = "ON"
@@ -283,7 +284,7 @@ class MqttSiren(MqttEntity, SirenEntity):
                     )
                     return
             self._update(process_turn_on_params(self, json_payload))
-            self.async_write_ha_state()
+            get_mqtt_data(self.hass).state_write_requests.write_state_request(self)
 
         if self._config.get(CONF_STATE_TOPIC) is None:
             # Force into optimistic mode.