IRI in search working

[vstarlinger]

This fixes #65

Search requests using IRIs will now default to use the graph_service to directly redirect to the correct concept or scheme. In case the IRI is not found in either the Concept or ConceptSchemes then it falls back to using the search on the full IRI string.

Uses

def _is_iri(query: str) -> bool:
    """Check if query string is a valid HTTP/HTTPS IRI."""
    try:
        parsed = rfc3987.parse(query.strip(), rule="IRI")
        return parsed.get("scheme") in ("http", "https")
    except ValueError:
        return False

to check if the query is a valid IRI