chore: update bibtexparser -> 2.0

[jennifer-richards]

Test-only library moved. Updates to use the new entry point / data model. Dropped some options we were setting that did not have obvious analogs. The test passed without those, so that seems to be ok.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.75%. Comparing base (e52df75) to head (56297b8).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #11737   +/-   ##
=======================================
  Coverage   88.75%   88.75%           
=======================================
  Files         337      337           
  Lines       45420    45420           
=======================================
  Hits        40311    40311           
  Misses       5109     5109           

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