Let \( \alpha \) and \( \beta \) be the real numbers such that \( \displaystyle\lim_{x \to 0} \dfrac{1}{x^{3}}\left( \dfrac{a}{2}\int_{0}^{x}\dfrac{1}{1-t^{2}}\,dt + \beta x \cos x \right)=2 \).Then the value of \( \alpha + \beta \) is________.
