all: use math/rand/v2 more

Updates #11058

Signed-off-by: Maisem Ali <maisem@tailscale.com>

util/cloudenv/cloudenv.go

@@ -8,7 +8,7 @@ import (
 	"context"
 	"encoding/json"
 	"log"
-	"math/rand"
+	"math/rand/v2"
 	"net"
 	"net/http"
 	"os"
@@ -74,8 +74,7 @@ func getDigitalOceanResolver() string {
 	// Randomly select one of the available resolvers so we don't overload
 	// one of them by sending all traffic there.
 	return digitalOceanResolver.Get(func() string {
-		rn := rand.New(rand.NewSource(time.Now().UnixNano()))
-		return digitalOceanResolvers[rn.Intn(len(digitalOceanResolvers))]
+		return digitalOceanResolvers[rand.IntN(len(digitalOceanResolvers))]
 	})
 }
 

util/reload/reload.go

@@ -9,7 +9,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
-	"math/rand"
+	"math/rand/v2"
 	"os"
 	"reflect"
 	"time"
@@ -73,7 +73,7 @@ func (r *ReloadOpts[T]) intervalWithJitter() time.Duration {
 		return tt
 	}
 
-	jitter := time.Duration(rand.Intn(int(r.IntervalJitter)))
+	jitter := rand.N(r.IntervalJitter)
 	return tt + jitter
 }
 

util/slicesx/slicesx.go

@@ -4,7 +4,7 @@
 // Package slicesx contains some helpful generic slice functions.
 package slicesx
 
-import "math/rand"
+import "math/rand/v2"
 
 // Interleave combines two slices of the form [a, b, c] and [x, y, z] into a
 // slice with elements interleaved; i.e. [a, x, b, y, c, z].
@@ -34,11 +34,11 @@ func Shuffle[S ~[]T, T any](s S) {
 	n := len(s)
 	i := n - 1
 	for ; i > 1<<31-1-1; i-- {
-		j := int(rand.Int63n(int64(i + 1)))
+		j := int(rand.N(int64(i + 1)))
 		s[i], s[j] = s[j], s[i]
 	}
 	for ; i > 0; i-- {
-		j := int(rand.Int31n(int32(i + 1)))
+		j := int(rand.N(int32(i + 1)))
 		s[i], s[j] = s[j], s[i]
 	}
 }