Hungary's premier-in-waiting, Peter Magyar, is keen to secure a return to the European Union mainstream and is moving quickly to mend fences. Part of that mission is a plan to have the country ready to join the euro by the end of the decade. Some, including the governor of the central bank, suggest that timeframe could be overly ambitious, given that outgoing Prime Minister Viktor Orban will hand over a sluggish economy and a fiscal mess. But if…