Update to math/rand/v2

This commit updates the uses of math/rand to math/rand/v2, which was
released in Go 1.22 (2024-02).

The new package is generally safer, see https://go.dev/blog/randv2 for
the details.

There are no user-visible changes, it is only adjusting the name of
functions, simplify some code thanks to v2 having a better API, etc.

internal/queue/queue.go

@@ -9,8 +9,9 @@ import (
 	"bytes"
 	"context"
 	"encoding/base64"
+	"encoding/binary"
 	"fmt"
-	"math/rand"
+	"math/rand/v2"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -67,17 +68,11 @@ var newID chan string
 
 func generateNewIDs() {
 	// The IDs are only used internally, we are ok with using a PRNG.
-	// We create our own to avoid relying on external sources initializing it
-	// properly.
-	prng := rand.New(rand.NewSource(time.Now().UnixNano()))
-
 	// IDs are base64(8 random bytes), but the code doesn't care.
 	buf := make([]byte, 8)
-	id := ""
 	for {
-		prng.Read(buf)
-		id = base64.RawURLEncoding.EncodeToString(buf)
-		newID <- id
+		binary.NativeEndian.PutUint64(buf, rand.Uint64())
+		newID <- base64.RawURLEncoding.EncodeToString(buf)
 	}
 }
 
@@ -485,7 +480,7 @@ func nextDelay(createdAt time.Time) time.Duration {
 
 	// Perturb the delay, to avoid all queued emails to be retried at the
 	// exact same time after a restart.
-	delay += time.Duration(rand.Intn(60)) * time.Second
+	delay += rand.N(60 * time.Second)
 	return delay
 }