\( \displaystyle \int_{0}^{\pi/4} \frac{\cos^2 x \,\sin^2 x}{\left(\cos^3 x + \sin^3 x\right)^2}\, dx \) is equal to:
\( \dfrac{1}{6} \)
\( \dfrac{1}{3} \)
\( \dfrac{1}{9} \)
\( \dfrac{1}{12} \)