By Kate Abnett BRUSSELS (Reuters) – European Union countries are wrangling over how to rapidly fill their gas storage ahead of next winter and share the burden of quickly buying large stocks at current sky-high prices. Europe is facing a race to build a buffer of stored gas ahead of winter, to help cope with potential supply disruptions and reduce the leverage of Russia. The country remains the EU’s top gas supplier even as Europe plans to phase out Russian fuels because of Moscow’s invasion of Ukraine. The European Commission last month proposed legislation requiring EU countries to fill thei…