Let \( f:\mathbb{R}\to\mathbb{R} \) be a function defined by \( f(x)=\dfrac{x}{\left(1+x^{4}\right)^{1/4}} \), and \( g(x)=f\!\left(f\!\left(f\!\left(f(x)\right)\right)\right) \). Then, \( \displaystyle18 \int_{0}^{\sqrt{2\sqrt{5}}} x^2 g(x) \, dx\) is equal to: