p2p/discover: add initial discovery v5 implementation (#20750)

This adds an implementation of the current discovery v5 spec.

There is full integration with cmd/devp2p and enode.Iterator in this
version. In theory we could enable the new protocol as a replacement of
discovery v4 at any time. In practice, there will likely be a few more
changes to the spec and implementation before this can happen.

p2p/discover/table_util_test.go

@@ -24,7 +24,6 @@ import (
 	"fmt"
 	"math/rand"
 	"net"
-	"reflect"
 	"sort"
 	"sync"
 
@@ -56,6 +55,23 @@ func nodeAtDistance(base enode.ID, ld int, ip net.IP) *node {
 	return wrapNode(enode.SignNull(&r, idAtDistance(base, ld)))
 }
 
+// nodesAtDistance creates n nodes for which enode.LogDist(base, node.ID()) == ld.
+func nodesAtDistance(base enode.ID, ld int, n int) []*enode.Node {
+	results := make([]*enode.Node, n)
+	for i := range results {
+		results[i] = unwrapNode(nodeAtDistance(base, ld, intIP(i)))
+	}
+	return results
+}
+
+func nodesToRecords(nodes []*enode.Node) []*enr.Record {
+	records := make([]*enr.Record, len(nodes))
+	for i := range nodes {
+		records[i] = nodes[i].Record()
+	}
+	return records
+}
+
 // idAtDistance returns a random hash such that enode.LogDist(a, b) == n
 func idAtDistance(a enode.ID, n int) (b enode.ID) {
 	if n == 0 {
@@ -173,9 +189,16 @@ func hasDuplicates(slice []*node) bool {
 }
 
 func checkNodesEqual(got, want []*enode.Node) error {
-	if reflect.DeepEqual(got, want) {
-		return nil
+	if len(got) == len(want) {
+		for i := range got {
+			if !nodeEqual(got[i], want[i]) {
+				goto NotEqual
+			}
+			return nil
+		}
 	}
+
+NotEqual:
 	output := new(bytes.Buffer)
 	fmt.Fprintf(output, "got %d nodes:\n", len(got))
 	for _, n := range got {
@@ -188,6 +211,10 @@ func checkNodesEqual(got, want []*enode.Node) error {
 	return errors.New(output.String())
 }
 
+func nodeEqual(n1 *enode.Node, n2 *enode.Node) bool {
+	return n1.ID() == n2.ID() && n1.IP().Equal(n2.IP())
+}
+
 func sortByID(nodes []*enode.Node) {
 	sort.Slice(nodes, func(i, j int) bool {
 		return string(nodes[i].ID().Bytes()) < string(nodes[j].ID().Bytes())