Let \( f(x) \) and \( g(x) \) be two functions satisfying \( f(x^2) + g(4 - x) = 4x^3 \) and \( g(4 - x) + g(x) = 0 \), then the value of \( \displaystyle \int_{-4}^{4} f(x^2) \, dx \) is ____________.