Function setup_addresses_in_network_namespace 

pub fn setup_addresses_in_network_namespace(
    addrs: &[CidrAddress],
    link_index: u32,
    new_name: &str,
    addr_client: &mut AddressClient,
) -> Result<(), NetworkError>

Core logic for setting up addresses in the new network namespace This function is extracted to make it testable without system calls

Note: The addresses passed to this function are already filtered in the main process to include only global scope and permanent addresses.