Fix ParticleFilter to work with set inputs

[johvincau]

Description

In #2964, it was pointed out that openmc.ParticleFilter, despite its documentation permitting sets (more broadly Iterables), throws a TypeError when given one. This PR fixes this issue.

The specific issue is that the attribute setter calls the function np.atleast_1d() on the input, which does not register sets as one-dimensional (and rightfully so, since sets don't have dimensions that can be indexed).

This function causes a set to be wrapped in a list, which causes issues with cv.check_iterable_type() since the depth of the iterable is increased beyond 1.

Quick Fix

Allowing set inputs for ParticleFilter seems uniquely appropriate, given its requirement for unique elements, and the rest of the code works fine with any iterable, set or not. In any case, only minor tweaks are required to make sets work.

I've opted to simply avoid calling np.atleast_1d() on sets, and use cv.check_type() which has extra provisions for checking if an Iterable contains a certain type in lieu of cv.check_iterable_type().

Side Issue

Despite its name, cv.check_iterable_type() only works on Sequences since it traverses the input with indexing. A more accurate name would probably be cv.check_sequence_type(), but then every other instance of this function must also be changed to reflect this.

Checklist

• I have performed a self-review of my own code
• I have run clang-format (version 15) on any C++ source files (if applicable)
• I have followed the style guidelines for Python source files (if applicable)
• I have made corresponding changes to the documentation (if applicable)
• I have added tests that prove my fix is effective or that my feature works (if applicable)

[paulromano]

I think the problem here is really that we should not be allowing any iterable object but rather we should only be accepting sequences (i.e., that can be indexed). With your patch here, the following does not work:

f1 = openmc.ParticleFilter({'photon', 'neutron'})
f1.bins[0]

Can you update this so that we only accept sequences?

[paulromano]

Thanks @johvincau!