add vendoring

vendor/github.com/getsentry/sentry-go/internal/crypto/randutil/randutil.go

@@ -0,0 +1,23 @@
+package randutil
+
+import (
+	"crypto/rand"
+	"encoding/binary"
+)
+
+const (
+	floatMax  = 1 << 53
+	floatMask = floatMax - 1
+)
+
+// Float64 returns a cryptographically secure random number in [0.0, 1.0).
+func Float64() float64 {
+	// The implementation is, in essence:
+	//	return float64(rand.Int63n(1<<53)) / (1<<53)
+	b := make([]byte, 8)
+	_, err := rand.Read(b)
+	if err != nil {
+		panic(err)
+	}
+	return float64(binary.LittleEndian.Uint64(b)&floatMask) / floatMax
+}