We call Exec on a PromQL Query here and here for query splitting and sharding, respectively, but never call Close on it.

This means that the PromQL engine can never release resources associated with the query. (At present, it returns a bunch of data structures to a pool, but this could change in the future.)

Fixing this isn't straightforward, as we currently use unsafe conversion to retain a reference to the query result until we encode it and send it to the caller. We'd likely need to add a cleanup mechanism to PrometheusResponse.