Type check all helpers (#25373)

* Type check all helpers, add inline exclusions for work in progress

* Remove unused Script._template_cache

* Add some missing type hints

* Remove unneeded type: ignore

* Type hint fixes

* Mypy assistance tweaks

* Don't look for None in deprecated config "at most once" check

* Avoid None name slugify attempt when generating entity id

* Avoid None state store attempt on entity remove

homeassistant/helpers/service.py

@@ -19,6 +19,9 @@ import homeassistant.helpers.config_validation as cv
 from homeassistant.util.async_ import run_coroutine_threadsafe
 from homeassistant.helpers.typing import HomeAssistantType
 
+
+# mypy: allow-incomplete-defs, allow-untyped-defs, no-check-untyped-defs
+
 CONF_SERVICE = 'service'
 CONF_SERVICE_TEMPLATE = 'service_template'
 CONF_SERVICE_ENTITY_ID = 'entity_id'