Smaller file segments is faster

[apete]

At this point it seems difficult to come up with a faster solution (and call it your own), but I believe I can make a contribution.

I took Sam Pullara's solution @spullara and changed one code line from

int numberOfSegments = Runtime.getRuntime().availableProcessors();

to

int numberOfSegments = 20 * Runtime.getRuntime().availableProcessors();

On my MacBook Air M2 Sam's solution takes about 5.6s. With that one line changed it's about 1s faster. 20 may not be the optimal number on another machine. The key thing is to make the segments smaller, and the number of segments a multiple of the number of cores.