Separated base_iri argument from triplestore_url in rdflib backend

[jesper-friis]

Before gave rdflib the base_iri argument an additional meaning not documented in Triplestore.init(). This is now taken over by the triplestore_url argument.

[codecov-commenter]

Codecov Report

Base: 73.32% // Head: 73.10% // Decreases project coverage by -0.22% ⚠️

Coverage data is based on head (9beba40) compared to base (f1039cb).
Patch coverage: 85.71% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #49      +/-   ##
==========================================
- Coverage   73.32%   73.10%   -0.23%     
==========================================
  Files          12       12              
  Lines         746      751       +5     
==========================================
+ Hits          547      549       +2     
- Misses        199      202       +3     

Impacted Files	Coverage Δ
tripper/backends/rdflib.py	89.39% <83.33%> (-4.16%)	⬇️
tripper/utils.py	84.15% <100.00%> (+0.15%)	⬆️

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[daniel-sintef]

I don't think backends should silently allow parameters they don't use. As this could confuse users (imagine one trying to figure out why the base_iri doesn't work, because they need to use triplestore_url).

I would suggest including a warning if the base_iri is provided, that it is unused.