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%	78, 137, 151, 197, 203–205, 229
iri_resolver.py	141	3	98%	311–312, 322
jsonld.py	2490	174	93%	241–245, 294, 331, 336, 346, 363–378, 414–415, 457, 465, 485, 493–494, 602–607, 687–688, 703–704, 764–769, 794–795, 810–811, 821–822, 848, 894, 903–909, 926, 968, 975, 982, 1047–1054, 1072, 1094–1096, 1106–1109, 1124, 1147, 1159–1162, 1258, 1267–1270, 1290, 1319, 1352, 1356, 1386–1391, 1404–1406, 1416–1418, 1461, 1480–1483, 1496, 1545, 1648–1655, 1682–1684, 1710–1713, 1889, 1927, 2233, 2364, 2373–2380, 2474, 2501, 2525, 2533, 3127, 3177, 3196, 3261, 3314, 3317, 3380, 3465, 3499, 3507, 3785, 3790, 3792, 3982–3984, 4133, 4196, 4431, 4719, 4851, 4885, 4914–4917, 4939–4940, 5123, 5187, 5214, 5288, 5290, 5308, 5406, 5455, 5687, 5689, 5728, 5730, 5739, 5881, 6009, 6096, 6216–6230, 6292, 6294, 6362, 6576, 6582–6586, 6625, 6628, 6718–6719, 6728
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	51	5	90%	56, 70, 82–90
TOTAL	3404	229	93%

Tests	Skipped	Failures	Errors	Time
1814	36 💤	0 ❌	0 🔥	2m 57s ⏱️