ref #7: [feat] add cleanup task

usecase/sandbox.py

@@ -84,7 +84,24 @@ class CleanupExpiredSandboxes:
         self._logger = logger
 
     def execute(self) -> list[SandboxSession]:
-        raise NotImplementedError
+        now = self._clock.now()
+        expired_sessions = self._repository.list_expired(now)
+        cleaned_sessions: list[SandboxSession] = []
+
+        for session in expired_sessions:
+            self._runtime.stop(session.container_id)
+            self._repository.delete(session.session_id)
+            cleaned_sessions.append(session)
+            self._logger.info(
+                'sandbox_cleaned',
+                attrs={
+                    'chat_id': session.chat_id,
+                    'session_id': session.session_id,
+                    'container_id': session.container_id,
+                },
+            )
+
+        return cleaned_sessions
 
 
 def _new_session_id() -> str: