fix(context): resolve prefixes from @Prefix declarations instead of IRI heuristic (#58)

Replace iri_to_domain_hint() with namespace binding lookup from
RDFLib's graph.namespaces() in context_generator.py. The @Prefix
declarations in the OWL Turtle source are the authoritative
prefix-to-namespace mappings - deriving prefix names by URL path
segment extraction was unreliable.

- Add _build_ns_prefix_lookup() and _lookup_prefix() helpers
- Use declared namespace bindings for domain and import prefixes
- Skip imports without @Prefix declaration (with warning, no guessing)
- Fix development to gx in envited-x and tzip21 contexts
- Update tests: add namespace lookup tests, add envited-x gx assertion

Signed-off-by: Carlo van Driesten <carlo.van-driesten@bmw.de>

Author: jdsika

artifacts/envited-x/envited-x.context.jsonld

@@ -16,7 +16,7 @@
       "skos": "http://www.w3.org/2004/02/skos/core#",
       "envited-x": "https://w3id.org/ascs-ev/envited-x/envited-x/v3/",
       "manifest": "https://w3id.org/ascs-ev/envited-x/manifest/v5/",
-      "development": "https://w3id.org/gaia-x/development#",
+      "gx": "https://w3id.org/gaia-x/development#",
       "hasCodeArtifact": {
          "@id": "envited-x:hasCodeArtifact",
          "@type": "@id"