Tens of thousands of Cubans crowded along Havana’s famed seawall on Friday to celebrate workers on their day, especially those who keep the socialist country powered. Employees of Cuba’s Electric Union are working 24 hours a day as the island’s power grid continues to crumble, provoking islandwide outages worsened by a lack of gasoline stemming from a U.S. energy blockade. “We are living through difficult times,” said Yunier Meriño Reyes, an accountant with the Electric Union who joined Friday’s march to celebrate his colleagues. “We are carrying out a very tough, arduous and relentless effort — day and night — to provide electricity to the people who need it.” Cuba’s power crisis deepened after the U.S. attacked Venezuela in early January, halting critical oil shipments from the South American country. Later that month, U.S. President Donald Trump threatened tariffs on any country that sells or provides oil to Cuba.…