docs: add class docstring to _LoopWrapper (#27870)

Document the purpose of the daemon thread that backs the sync
branch of the timeout decorator.

Co-authored-by: oss-agent-shin <279349115+oss-agent-shin@users.noreply.github.com>

litellm/timeout.py

@@ -90,6 +90,13 @@ def timeout(timeout_duration: float = 0.0, exception_to_raise=Timeout):
 
 
 class _LoopWrapper(Thread):
+    """Daemon thread that owns a dedicated asyncio event loop.
+
+    Used by the sync branch of :func:`timeout` to run a coroutine on a
+    background event loop so the calling thread can wait on it with a
+    timeout via :func:`asyncio.run_coroutine_threadsafe`.
+    """
+
     def __init__(self):
         super().__init__(daemon=True)
         self.loop = asyncio.new_event_loop()