Restore service call performance by avoiding expensive runtime cast (#143378)

Improve service call performance by avoiding expensive runtime type checking

Most of the overhead here was casting

homeassistant/helpers/config_validation.py

@@ -21,7 +21,7 @@ from socket import (  # type: ignore[attr-defined]  # private, not in typeshed
     _GLOBAL_DEFAULT_TIMEOUT,
 )
 import threading
-from typing import Any, cast, overload
+from typing import TYPE_CHECKING, Any, cast, overload
 from urllib.parse import urlparse
 from uuid import UUID
 
@@ -355,7 +355,13 @@ def ensure_list[_T](value: _T | None) -> list[_T] | list[Any]:
     """Wrap value in list if it is not one."""
     if value is None:
         return []
-    return cast(list[_T], value) if isinstance(value, list) else [value]
+    if isinstance(value, list):
+        if TYPE_CHECKING:
+            # https://github.com/home-assistant/core/pull/71960
+            # cast with a type variable is still slow.
+            return cast(list[_T], value)
+        return value  # type: ignore[unreachable]
+    return [value]
 
 
 def entity_id(value: Any) -> str: