Add bpz files; reduce duplicated logic in if/else

[OliviaLynn]

Problem & Solution Description (including issue #)

For the bpz portion of rail#48.

• I wasn't 100% sure if we wanted to keep the other (non-tar) data separate like the tar data.

• If downloading test_dc2_training_9816_broadtypes.hdf5 and test_dc2_train_customtemp_broadttypes.hdf5 from NERSC along with the tar works for people, here's a PR for that.

• This PR also reduces the duplicated logic across the if/else branching.

Code Quality

• [x] My code follows the code style of this project
• [x] I have written unit tests or justified all instances of #pragma: no cover; in the case of a bugfix, a new test that breaks as a result of the bug has been added
• [x] My code contains relevant comments and necessary documentation for future maintainers; the change is reflected in applicable demos/tutorials (with output cleared!) and added/updated docstrings use the NumPy docstring format
• [x] Any breaking changes, described above, are accompanied by backwards compatibility and deprecation warnings

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (263b2a6) 96.96% compared to head (e125207) 96.96%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #76 +/- ## ======================================= Coverage 96.96% 96.96% ======================================= Files 32 32 Lines 1714 1714 ======================================= Hits 1662 1662 Misses 52 52 ```

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