nextDoubleFast

Reads a double value from the input stream, trading up to 1 ulp of accuracy for speed on high precision input. For values with at most ~15 significant digits (most input) this is identical to nextDouble(): same exact result, same speed. For 16+ significant digits, such as the full precision output of Double.toString, nextDouble() falls back to Double.parseDouble to stay exact, while this method keeps the fast path and may be off by 1 ulp (~2x faster).