Allow plugins to execute a background query

[MathiasVDA]

Needed for: Matdata-eu/yasgui-graph-plugin#10

[MathiasVDA]

We’re building a YASR visualization plugin (Graph plugin) that can expand nodes on click by running a follow-up SPARQL query (e.g., DESCRIBE or a small CONSTRUCT around the clicked resource) in the background and then merging the returned triples into the visualization.

Today, a YASR plugin only has access to the YASR instance and the current results (e.g., yasr.results.getBindings() and yasr.resultsEl). This is enough to render current results, but not enough to reliably execute new SPARQL queries because the plugin cannot access:

• the active tab’s endpoint / requestConfig (headers/auth, method, default graphs, etc.)
• a supported way to run a query through the same execution pipeline YASGUI uses

As a result, plugins would need to duplicate request logic with fetch, which breaks consistency and complicates auth/proxy handling.

Expose something like:

• yasr.executeQuery(query: string, opts?: { requestConfigOverride?: Partial }) => Promise<YasrResultsLike | RawResponse>

The implementation should reuse the same endpoint + requestConfig as the current YASGUI tab (YASQE/YASGUI).

Acceptance criteria

• A YASR plugin can, on user interaction, run a new SPARQL query without hardcoding an endpoint and without duplicating request logic.
• The background query uses the same requestConfig as the active YASGUI tab (endpoint, headers/auth, method, etc.).
• The API is documented as part of the plugin interface (what’s stable, what isn’t).
• cancellation support (abort previous expansion query when user clicks a different node