fix: resolve mypy type errors in llm.py

- Replace Lock._loop private attribute access with explicit loop tracking
- Add explicit type annotation for clients_to_close list in shutdown()

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

django/aiservice/aiservice/llm.py

@@ -76,6 +76,7 @@ class LLMClient:
         self.client_loop: asyncio.AbstractEventLoop | None = None
         self.background_tasks: set[asyncio.Task[Any]] = set()
         self._client_lock: asyncio.Lock | None = None
+        self._client_lock_loop: asyncio.AbstractEventLoop | None = None
 
     async def call(
         self,
@@ -96,8 +97,9 @@ class LLMClient:
         loop = asyncio.get_running_loop()
 
         # Create lock for this event loop if it doesn't exist
-        if self._client_lock is None or self._client_lock._loop is not loop:
+        if self._client_lock is None or self._client_lock_loop is not loop:
             self._client_lock = asyncio.Lock()
+            self._client_lock_loop = loop
 
         if loop is not self.client_loop:
             async with self._client_lock:
@@ -243,7 +245,7 @@ class LLMClient:
         This method ensures all clients are explicitly closed during graceful shutdown,
         before the event loop is torn down.
         """
-        clients_to_close = []
+        clients_to_close: list[tuple[str, AsyncAzureOpenAI | AsyncAnthropicBedrock]] = []
 
         if self.openai_client is not None:
             clients_to_close.append(("OpenAI", self.openai_client))