Convert test_rdflib_dumper.py from unittest to pytest

[vladistan]

• Convert setUp methods to pytest fixtures (prefix_map, converter_prefix_map, issue_429_graph)
• Convert all 13 test methods from 2 classes to standalone functions
• Convert _check_objs from instance method to helper function

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.38%. Comparing base (c5bec6e) to head (1571cf8).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #427      +/-   ##
==========================================
- Coverage   77.45%   77.38%   -0.07%     
==========================================
  Files          52       52              
  Lines        4479     4479              
  Branches      979      979              
==========================================
- Hits         3469     3466       -3     
- Misses        783      785       +2     
- Partials      227      228       +1     

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[ialarmedalien]

Remove the cruft; using pytest's parametrize to run the same test with different inputs.

[sierra-moxon]

@ialarmedalien - I'd like to get this into the release candidate today - is your review still blocking here?

[ialarmedalien]

Nope, sorry for the delay in re-reviewing!