Executes a SPARQL SELECT query against an in-memory RDF.Graph via the sparql library and reshapes results into plain maps keyed by column name (mirroring the row shape ggen's own Tera templates already consume).

Disclosed limitation, empirically confirmed (not just asserted): the sparql hex package (v0.3.12, the default --engine sparql used by this module) does not correctly honor ORDER BY. A join-shaped query mirroring the real gate fixtures (?field ex:fieldOf ?entity ; ex:fieldOrder ?field_order . ?entity ex:entityStruct ?entity_struct . with ORDER BY ?field_order over 10 rows) came back in reverse order ([9, 8, 7, 6, 5, 4, 3, 2, 1, 0] instead of the requested ascending [0, 1, ..., 9]) when run through run/2. The same query run through GgenIgniter.Query.Oxigraph.run/2 (a real, independent, spec-conformant SPARQL 1.1 engine) returned the correct ascending order. If row order matters for a query, use --engine oxigraph instead of the default --engine sparql.