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/test/test_ci.sh

@@ -0,0 +1,55 @@
+#!/usr/bin/env bash
+
+BUILD_DIR=$(pwd)
+echo "PATH=$PATH" > "$BUILD_DIR/test/.tpkg.var.master"
+
+if git log HEAD^..HEAD | grep -q 'git:TEST [0-9][0-9]*'
+then
+	ONLY_TEST=$(git log HEAD^..HEAD | grep 'git:TEST [0-9][0-9]*' | sed 's/^.*git:TEST \([0-9][0-9]*\).*$/\1/g')
+else
+	ONLY_TEST=""
+fi
+
+if git log HEAD^..HEAD | grep -q 'git:REGRESSION'
+then
+	NO_REGRESSION=0
+else
+        NO_REGRESSION=1
+fi
+
+if [ -z "$TPKG" ] || [ ! -x "$TPKG" ]
+then
+        if [ -x tpkg/tpkg ]		; then TPKG="$(pwd)/tpkg/tpkg"
+        elif [ -x test/tpkg/tpkg ]	; then TPKG="$(pwd)/test/tpkg/tpkg"
+        elif command -v tpkg > /dev/null; then TPKG="$(command -v tpkg)"
+        else
+                echo Did not find tpkg program!
+                exit 255    # Shell can only return 0-255
+        fi
+fi
+
+# RUN THE TESTS
+for tests in "$BUILD_DIR"/test/*.tpkg
+do
+	TESTFN="$(basename "$tests")"
+	TESTNR=${TESTFN%-*}
+	[ -n "$ONLY_TEST" ] && [ x"$ONLY_TEST" != x"$TESTNR" ] && continue
+	case "$TESTNR" in
+	[3-5][0-9]*)	[ $NO_REGRESSION = 1 ] && continue
+			;;
+	esac
+	case $TESTNR in
+	02)	# splint doesn't work on linux
+		[ "x$(uname -s)" = "xLinux" ] && continue
+		;;
+	32)	# No backwards compatibility regression testing 
+		# when .so had major version bump.
+		chmod +x "$BUILD_DIR/packaging/ldns-config"
+		BINAPI=$("$BUILD_DIR/packaging/ldns-config" --libversion)
+		[ "x${BINAPI#*.}" = "x0.0" ] && continue
+	esac
+	$TPKG -b "$BUILD_DIR/test" -a "$BUILD_DIR" exe "$TESTFN"
+done
+
+cd test || { echo "Where is the test directory?"; exit 1; }
+exec $TPKG -n -1 r