You're doing quite a lot of copying, which - it seems - is mostly unnecessary. For example, your next() method

sub next {
    my $self = shift;
    my @urls = @{$self->{urls}};
    
    if (!@urls) {
        return undef;
    }
    my $url = pop(@urls);
    
    
    $self->{urls} = \@urls;
    return $url;
}
[download]

could also be written as

sub next {
    my $self = shift;
    return pop @{$self->{urls}};
}
[download]

which should be functionally equivalent...  Similarly add().