Description

Currently, if you run a model with a tally that has a DistribcellFilter and try to use apply_tally_results=True, it raises an exception if you try to look at the tally results because the number of bins on the filter is not populated. This PR fixes it by making the following updates:

• The number of bins for DistribcellFilters is now populated in the Tally._read_results method.
• When a model is exported to XML, each Tally is marked with a _model attribute that references the Model that holds it, and each Filter is marked with a _tally attribute that references one of the tallies that holds it. This makes it so that we can determine geometry paths to cell instances, which are used when calling get_pandas_dataframe on a tally that includes a DistribcellFilter

A few other miscellaneous fixes are included in this PR:

• When using apply_tally_results=True, if you look at the shape attribute of a tally, it has zero for the middle dimension (nuclides) when no nuclides are specified. Now it will show 1, corresponding to the default of "total".
• The SearchResult class was not showing up in the openmc namespace because it wasn't specifically imported from openmc.model.
• Make use of gnds_name where possible

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)