Speed up ZHA initialization and improve startup responsiveness (#108103)

* Limit concurrency of startup traffic to allow for interactive usage

* Drop `retryable_req`, we already have request retrying

* Oops, `min` -> `max`

* Add a comment describing why `async_initialize` is not concurrent

* Fix existing unit tests

* Break out fetching mains state into its own function to unit test

tests/components/zha/conftest.py

@@ -135,7 +135,7 @@ def _wrap_mock_instance(obj: Any) -> MagicMock:
         real_attr = getattr(obj, attr_name)
         mock_attr = getattr(mock, attr_name)
 
-        if callable(real_attr):
+        if callable(real_attr) and not hasattr(real_attr, "__aenter__"):
             mock_attr.side_effect = real_attr
         else:
             setattr(mock, attr_name, real_attr)