fix: return W3C standard JSON format for SPARQL ASK queries

ASK queries were returning raw JavaScript booleans (true/false) instead of
the W3C SPARQL 1.1 standard JSON format {"head": {}, "boolean": true/false}.

This fix uses QueryResultsSerializer to properly format ASK query results,
ensuring compatibility with standards-compliant SPARQL applications and
consistency with SELECT/CONSTRUCT query behavior.

The issue was in ng-verifier/src/request_processor.rs where
AppResponseV0::True/False were returned instead of a properly
serialized QueryResult.

Fixes: Non-standard ASK query responses
Reference: https://www.w3.org/TR/sparql11-results-json/

ng-verifier/src/request_processor.rs

@@ -294,11 +294,13 @@ impl Verifier {
                 ))
             }
             QueryResults::Boolean(b) => {
-                if b {
-                    AppResponse::V0(AppResponseV0::True)
-                } else {
-                    AppResponse::V0(AppResponseV0::False)
-                }
+                // FIX: Serialize boolean results as standard SPARQL JSON format
+                // instead of returning AppResponseV0::True/False
+                let serializer = QueryResultsSerializer::from_format(QueryResultsFormat::Json);
+                let result = serializer
+                    .serialize_boolean_to_write(Vec::new(), b)
+                    .map_err(|_| "QueryResult serializer error")?;
+                AppResponse::V0(AppResponseV0::QueryResult(result))
             }
             QueryResults::Graph(quads) => {
                 let mut results = vec![];