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/nettrace/trace.go

@@ -5,7 +5,7 @@ package nettrace
 import (
 	"container/ring"
 	"fmt"
-	"math/rand"
+	"math/rand/v2"
 	"sort"
 	"strconv"
 	"strings"