all: replace internal rand shim with math/rand/v2

lapack/testlapack/dlangb_bench.go

@@ -7,15 +7,15 @@ package testlapack
 import (
 	"fmt"
 	"math"
+	"math/rand/v2"
 	"testing"
 
-	"gonum.org/v1/gonum/internal/rand"
 	"gonum.org/v1/gonum/lapack"
 )
 
 func DlangbBenchmark(b *testing.B, impl Dlangber) {
 	var result float64
-	rnd := rand.New(rand.NewSource(1))
+	rnd := rand.New(rand.NewPCG(1, 1))
 	for _, bm := range []struct {
 		n, k int
 	}{