logtail: add a few new methods to PublicID

These are for use in our internal systems.

Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>

logtail/id.go

@@ -7,6 +7,7 @@
 import (
 	"crypto/rand"
 	"crypto/sha256"
+	"encoding/binary"
 	"encoding/hex"
 	"errors"
 	"fmt"
@@ -156,3 +157,21 @@ func fromHexChar(c byte) (byte, bool) {
 
 	return 0, false
 }
+
+func (id1 PublicID) Less(id2 PublicID) bool {
+	for i, c1 := range id1[:] {
+		c2 := id2[i]
+		if c1 != c2 {
+			return c1 < c2
+		}
+	}
+	return false // equal
+}
+
+func (id PublicID) IsZero() bool {
+	return id == PublicID{}
+}
+
+func (id PublicID) Prefix64() uint64 {
+	return binary.BigEndian.Uint64(id[:8])
+}