Parallelize Calling the Parameterization in IrisZo

[cohnt]

When requesting a region that has a very small fraction in collision from IrisZo, there will be a huge number of samples required to pass the statistical test. If the user has also specified a parameterization function, a lot of time might be needed to remap those particles. If the parameterization function is threadsafe, we should take advantage, as this can easily be parallelized.