Fix PR review issues: remove unused event, use specific exception

Author: abhishek-anand

coderunner/client.py

@@ -122,7 +122,7 @@ def health(self) -> bool:
         try:
             response = self._client.get(f"{self.base_url}/health")
             return response.status_code == 200
-        except Exception:
+        except httpx.RequestError:
             return False
 
     def close(self):

server.py

@@ -338,8 +338,6 @@ async def _health_check_loop(self):
 
 # --- GRACEFUL SHUTDOWN ---
 
-_shutdown_event = asyncio.Event()
-
 
 async def graceful_shutdown():
     """Clean up kernels on shutdown."""