The state’s longest serving attorney general is heading to Big Law.About nine months after leaving office, former Illinois attorney general Lisa M. Madigan has joined Kirkland & Ellis LLP as a litigation partner.Madigan said she’s ready for the next chapter of her career.“Kirkland offered me a unique opportunity to work on complex issues that I have spent much of my career working on. The firm has a great reputation and I am excited about the opportunity to work on litigation, internal investigations …