fix: populate ldns submodule and add autotools to LDNS build stage

- Re-cloned zonemaster-ldns with --recurse-submodules so the bundled
  ldns C library source (including Changelog and configure.ac) is present
- Added autoconf, automake, libtool to Dockerfile.backend ldns-build stage
  so libtoolize + autoreconf can generate ldns/configure during make

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

zonemaster-ldns/ldns/contrib/DNS-LDNS/lib/DNS/LDNS/DNSSecTrustTree.pm

@@ -0,0 +1,99 @@
+package DNS::LDNS::DNSSecTrustTree;
+
+use 5.008008;
+use strict;
+use warnings;
+
+use DNS::LDNS;
+
+our $VERSION = '0.61';
+
+sub add_parent {
+    my ($self, $parent, $sig, $parent_status) = @_;
+
+    if (DNS::LDNS::GC::is_owned($parent)) {
+	die "Cannot add to multiple trees.";
+    }
+    my $s = _add_parent($self, $parent, $sig, $parent_status);
+    DNS::LDNS::GC::own($parent, $self);
+    $DNS::LDNS::last_status = $s;
+    return $s;
+}
+
+sub contains_keys {
+    my ($self, $trusted_keys) = @_;
+
+    my $s = _contains_keys($self, $trusted_keys);
+    $DNS::LDNS::last_status = $s;
+    return $s;
+}
+
+sub rr {
+    my $self = shift;
+    return DNS::LDNS::GC::own($self->_rr, $self);
+}
+
+sub rrset {
+    my $self = shift;
+    return DNS::LDNS::GC::own($self->_rrset, $self);
+}
+
+sub parent {
+    my ($self, $i) = @_;
+    return DNS::LDNS::GC::own($self->_parent($i), $self);
+}
+
+sub parent_status {
+    my ($self, $i) = @_;
+    my $s = _parent_status($self, $i);
+    $DNS::LDNS::last_status = $s;
+    return $s;
+}
+
+sub parent_signature {
+    my ($self, $i) = @_;
+    return DNS::LDNS::GC::own($self->_parent_signature($i), $self);
+}
+
+1;
+__END__
+
+=head1 NAME
+
+DNS::LDNS::DNSSecTrustTree - Trust tree from signed RR to trust anchors
+
+=head1 SYNOPSIS
+
+  use DNS::LDNS ':all'
+
+  tree = new DNS::LDNS::DNSSecTrustTree
+  tree->print(fp)
+  d = tree->depth
+  status = tree->add_parent(parent, sig, parent_status)
+  status = tree->contains_keys(trusted_keys)
+
+  # Node attributes
+  rr = tree->rr;
+  rrset = tree->rrset
+  ptree = tree->parent(i)
+  pstatus = tree->parent_status(i)
+  rr = tree->parent_signature(i)
+  count = tree->parent_count
+
+=head1 SEE ALSO
+
+http://www.nlnetlabs.nl/projects/ldns
+
+=head1 AUTHOR
+
+Erik Pihl Ostlyngen, E<lt>erik.ostlyngen@uninett.noE<gt>
+
+=head1 COPYRIGHT AND LICENSE
+
+Copyright (C) 2013 by UNINETT Norid AS
+
+This library is free software; you can redistribute it and/or modify
+it under the same terms as Perl itself, either Perl version 5.14.2 or,
+at your option, any later version of Perl 5 you may have available.
+
+=cut