Digital-payments pioneer PayPal is in a yearslong rut. Enrique Lores is tasked with saving it. The 61-year-old was named chief executive of PayPal earlier this year after decades at HP and its predecessor company, Hewlett-Packard, which he played a key role in splitting up. Lores has since announced an ambitious turnaround plan for PayPal that includes reorganizing its business lines and slashing at least $1.5 billion in costs—moves reminiscent of the playbook he has deployed in his previous roles. Now, one of PayPal’s rivals has lobbed a buyout offer. undefined undefined Payments company Stripe and private-equity firm Advent International have…