Migrate JsonLdProcessor to RDFLib

[mielvds]

This PR migrates JsonLdProcessor to rdflib and completes the internal migration to rdflib. It introduces a legacy mode to preserve backward-compatibility of the public API.

Changed

• Migrated jsonld.to_rdf(), jsonld.from_rdf(), and N-Quads parsing/serialization to use rdflib.Dataset and RDFLib terms directly.
  • jsonld.to_rdf() now returns an rdflib.Dataset by default when no output format is requested.
  • Added legacyMode to jsonld.to_rdf() to return the previous RDF.js-like dataset dict.
  • jsonld.from_rdf() now accepts both rdflib.Dataset inputs and the previous legacy dataset dict shape.
• N-Quads input/output now delegates to RDFLib instead of PyLD’s custom parser and serializer.

Removed

• Removed the internal pyld.nquads parser/serializer module.

Fixed

• Preserved RDF literal lexical forms when converting through RDFLib, including canonical double output, large numeric values, and compound literal handling.
• Fixed iri_resolver.unresolve() query/fragment reconstruction while cleaning up the resolver docstring.

Maintenance

• Updated RDF-related tests for RDFLib dataset and N-Quads serialization behavior.
• Removed small Python 2-era compatibility code and simplified a few internal collection checks.

[github-actions]

Coverage Report

File	Stmts	Miss	Cover	Missing
lib/pyld
canon.py	279	15	95%	35, 46, 49–54, 78–79, 508, 530, 594, 604, 658–659
context_resolver.py	103	8	92%	78, 137, 151, 197, 203–205, 229
iri_resolver.py	141	3	98%	311–312, 322
jsonld.py	2487	173	93%	244–248, 297, 334, 339, 349, 366–381, 417–418, 460, 468, 488, 496–497, 605–610, 690–691, 706–707, 767–772, 797–798, 813–814, 824–825, 851, 897, 906–912, 929, 971, 978, 985, 1050, 1075, 1097–1099, 1109–1112, 1127, 1150, 1162–1165, 1261, 1270–1273, 1293, 1322, 1355, 1359, 1392–1397, 1410–1412, 1422–1424, 1467, 1486–1489, 1502, 1551, 1654–1661, 1688–1690, 1716–1719, 1895, 1933, 2239, 2370, 2379–2386, 2480, 2507, 2531, 2539, 3133, 3183, 3202, 3267, 3320, 3323, 3386, 3471, 3505, 3513, 3791, 3796, 3798, 3988–3990, 4139, 4202, 4437, 4725, 4857, 4891, 4920–4923, 4945–4946, 5129, 5193, 5220, 5294, 5296, 5314, 5412, 5461, 5693, 5695, 5734, 5736, 5745, 5887, 6015, 6102, 6222–6236, 6298, 6300, 6368, 6582, 6588–6592, 6631, 6634, 6724–6725, 6734
util.py	72	3	96%	43, 116, 136
lib/pyld/documentloader
aiohttp.py	71	22	69%	29–39, 68, 74, 86, 98–106, 118–121, 138, 153–156
file.py	36	1	97%	49
requests.py	52	5	90%	57, 71, 83–91
scheme_directed.py	15	1	93%	38
TOTAL	3466	231	93%

Tests	Skipped	Failures	Errors	Time
1839	36 💤	0 ❌	0 🔥	1m 20s ⏱️

[mielvds]

@anatoly-scherbakov et al. would you mind doing an in-depth review of the changes to jsonld.py? The changes should be overseeable, but they are crucial to making the switch to 4.0 and rdflib.