- Instead of just computing the nnz of L and U, the CSR `row_ptrs`
  are computed in the first kernel, allowing for better parallelization
- Now checking if the `system_matrix` given to factory is square
  (including a test that checks if it is working)
- Fixed errors in omp test (leading to a lower epsilon in comparison)

- Use a strategy object (the default one that is used if no strategy
  is provided) in ParIlu
- parallized the omp `initialize_row_ptrs_l_u` kernel

- Added additional test with more iterations for OpenMP ParIlu test
  (Therefore, creating a function `compute_lu` to simplify that)
- Renaming variables to better fit their purpose