Import in the executor by default for core integrations (#112127)

* Import in the executor by default for core integration

* merge correct branch in

* Group loading of platforms in the import executor

* adjust test

* remove other pr

* Fix async_prepare_setup_platform test

The message changed because the order changed but was not caught before
merge because it required the combination of PRs to change
the error message

* fix

* tweak

* fix

* self review

* review

* fix hue mocking

* Update homeassistant/loader.py

Co-authored-by: Paulus Schoutsen <balloob@gmail.com>

* lint

* Fix async_get_component loading in the executor when the module is already loaded

The sys.modules check was incorrect (only on dev)

* fix

* Avoid multiple executor jobs with concurrent calls to async_get_component

Return a future that can be awaited if the component is
curently being loaded

* adjust

* coverage

* coverage

* concurrent platforms load test

* doc strings

* coverage

---------

Co-authored-by: Paulus Schoutsen <balloob@gmail.com>

homeassistant/loader.py

@@ -742,7 +742,10 @@ class Integration:
     @cached_property
     def import_executor(self) -> bool:
         """Import integration in the executor."""
-        return self.manifest.get("import_executor") or False
+        # If the integration does not explicitly set import_executor, we default to
+        # True if it's a built-in integration and False if it's a custom integration.
+        # In the future, we want to default to True for all integrations.
+        return self.manifest.get("import_executor", self.is_built_in)
 
     @property
     def mqtt(self) -> list[str] | None: