Over the last four years, alone on the witness stand in federal court or huddled in back rooms with federal agents, Mani Chulpayev has turned in what federal officials have called one of the most remarkable mob turncoat performances in memory. He has testified about an arson that leveled an entire block in Queens, about multiple extortions backed by beatings, about kidnappings, rampant Medicaid fraud, jewelry theft and trafficking in prostitutes. Certainly, he's been productive. But they are also hobbled by a culture of betrayal.