Create a base set of toRdf / fromRdf test cases

[Ostrzyciel]

Add a set of tests checking the conversion from N-Quads/N-Triples to Jelly and vice versa.

Use JSON-LD tests as inspiration:

• Docs: https://w3c.github.io/json-ld-api/reports/
• GitHub: https://github.com/w3c/json-ld-api/tree/main/tests

Directory structure:

• tests (at the root of this repo)
  • fromRdf (test group name)
    • triples_001 (test identifier)
      • in_001.nt
      • out.jelly
    • quads_001
      • in_001.nq (stream element 1)
      • in_002.nq (stream element 2)
      • out.jelly

Note that the implementing the test metadata or reporting mechanisms is not part of this issue. This can be done later as another subissue of #25.

We can make test subgroups based on feature support (e.g., RDF-star, generalized RDF, namespace declarations).

CC-ing @adanilenka and @bswck as this will be useful in pyjelly.