Castleton Commodities International will buy Morgan Stanley’s physical oil business, the largest and oldest on Wall Street, vaulting the Connecticut-based merchant into the big leagues of global crude and fuel traders. In a long-awaited deal that appears to mark the end of the Wall Street bank’s more than three-decade history as a major player in physical oil markets, Castleton will gain several dozen oil tank storage leases, physical oil supply and purchase contracts, and a team of about a hundred traders.