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.

[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%	76, 135, 149, 195, 201–203, 227
iri_resolver.py	141	3	98%	307–308, 318
jsonld.py	2489	173	93%	262–266, 349, 386, 391, 401, 418–433, 469–470, 512, 520, 540, 548–549, 657–662, 742–743, 758–759, 819–824, 849–850, 865–866, 876–877, 903, 949, 958–964, 981, 1023, 1030, 1037, 1102, 1127, 1149–1151, 1161–1164, 1179, 1202, 1214–1217, 1309, 1321–1324, 1344, 1373, 1406, 1410, 1440–1445, 1458–1460, 1470–1472, 1515, 1534–1537, 1546, 1595, 1698–1705, 1732–1734, 1760–1763, 1939, 1977, 2385, 2394–2401, 2493, 2520, 2543, 2552, 3132, 3182, 3201, 3266, 3319, 3322, 3385, 3470, 3504, 3512, 3790, 3795, 3797, 3846, 3988–3990, 4122, 4185, 4420, 4708, 4842, 4876, 4905–4908, 4934–4935, 5118, 5182, 5209, 5283, 5285, 5303, 5401, 5450, 5682, 5684, 5723, 5725, 5734, 5873, 6001, 6088, 6208–6222, 6284, 6286, 6354, 6567, 6573–6577, 6616, 6619, 6709–6710, 6719
util.py	63	2	97%	41, 114
lib/pyld/documentloader
aiohttp.py	71	22	69%	29–39, 68, 74, 86, 98–106, 118–121, 138, 153–156
requests.py	49	5	90%	54, 68, 80–88
TOTAL	3264	228	93%

Tests	Skipped	Failures	Errors	Time
1798	43 💤	0 ❌	0 🔥	2m 54s ⏱️