This exercise is a simple implementation of the Mandelbrot set using rayon library.
The standard library's spawn function is an important primitive, but it's not designed specifically for fork-join parallelism. Better fork-join APIs have been built on top of it. One of the most popular is the rayon library, which provides a data parallelism API. It allows you to parallelize operations on collections, such as arrays and vectors, with minimal effort. You should change the code to use rayon library to calculate the Mandelbrot set faster.