OutboundLanes: StorageDescriptor<
    [Key: FixedSizeBinary<4>],
    {
        latest_generated_nonce: bigint;
        latest_received_nonce: bigint;
        oldest_unpruned_nonce: bigint;
        state: Enum<{ Closed: undefined; Opened: undefined }>;
    },
    true,
    never,
>

Map of lane id => outbound lane data.