size_t is needed for some variables in parsec_tiled_matrix_t

In quantum simulation using the state-vector representation, the system’s data is stored as a very large vector of length (2^n), where n is the number of qubits. Because of the communication patterns involved, it is cumbersome and inefficient to reorganize this data into a matrix form, leading to some variables in parsec_tiled_matrix_t bigger than INT_MAX.
