The southern border and immigration have emerged as fiercely contested issues as the Long Island congressional special election to replace disgraced ex-Rep. George Santos starts to heat up. Republican Mazi Melesa Pilip and Democratic ex-Rep. Tom Suozzi held dueling news conferences and TV ads on the issue last week as the Feb. 13 election edges closer. Democratic groups have so fardramatically outspent their GOP rivals, raising questions about how hard Republicans are fighting to hold on to the swing seat on the North Shore and a slice of Queens. Republicans may be counting on the vaunted GOP …