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/config_entry_flow.py

@@ -4,6 +4,8 @@ from functools import partial
 from homeassistant import config_entries
 
 
+# mypy: allow-incomplete-defs, allow-untyped-defs
+
 def register_discovery_flow(domain, title, discovery_function,
                             connection_class):
     """Register flow for discovered integrations that not require auth."""