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

• My code follows the code style of this project
• 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
• 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
• Any breaking changes, described above, are accompanied by backwards compatibility and deprecation warnings

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

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

Additional details and impacted files

@@           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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[sschmidt23]

Looks good, thanks Olivia