The European Central Bank’s latest offer of free cash to lenders attracted little interest on Thursday, in a sign of just how much liquidity is already sloshing around the financial system. An offer for three-year loans — at a rate that starts at zero and could fall as low as the deposit rate, currently minus 0.5% — was taken up by 28 banks for a total of just 3.4 billion euros ($3.8 billion), well below predictions of 20-100 billion euros.