Let \( A \) be a square matrix such that \( AA^{T} = I \). Then \( \frac{1}{2} A \left[ (A + A^{T})^{2} + (A - A^{T})^{2} \right] \) is equal to:
\( A^{3} + I \)
\( A^{3} + A^{T} \)
\( A^{2} + I \)
\( A^{2} + A^{T} \)