* 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
