Function build_operational_service 

pub fn build_operational_service(
    compressed_fabric_id: [u8; 8],
    node_id: u64,
    addresses: Vec<IpAddr>,
    port: u16,
) -> MatterService

Build the operational _matter._tcp mDNS record to advertise so a requestor can resolve us. Instance name is <compressed-fabric-id>-<node-id> in uppercase hex (Matter Core §4.3.1), matching what the controller’s initiator resolves against via operational_instance_name.