Merge joins without using RDF4J API

[ate47]

Part of the endpoint? (leave empty if you don't know)

• Backend (qendpoint-backend)
• Store (qendpoint-backend)
• Core (qendpoint-core)
• Frontend (qendpoint-frontend)
• Other

Description of the request

(it's just an issue to get an ID)

As show in previous experiments, the added overhead of RDF4J is what costs us most of the runtime, maybe with can group the TP search with an optimizer and ignore the RDF4J joins while emiting the variable directly

Do I want to contribute to make it?

Yes

Something else?

No response