Function fetch_relay_parent_info 

pub async fn fetch_relay_parent_info<Sender>(
    sender: &mut Sender,
    query_at: Hash,
    session_index: SessionIndex,
    relay_parent: Hash,
) -> Result<Option<RelayParentInfo<Hash, BlockNumber>>, Error>
where
    Sender: SubsystemSender<RuntimeApiMessage> + SubsystemSender<ChainApiMessage>,

Fetch relay parent info for a block, including the block being queried at.

Works for all blocks within the max_relay_parent_session_age window, including the self-query case (query_at == relay_parent). For ancestors, uses the ancestor_relay_parent_info runtime API. For self, constructs the answer from the block header and session check.

Requires both RuntimeApiMessage and ChainApiMessage senders.