test(multivector): Update unit test to expect @ prefix in scoring formula

Fixed MultiVectorQueryTest to expect the correct Redis aggregation syntax with @ prefix.

The scoring formula needs @ prefix when referencing fields created by APPLY in Redis
aggregation queries. Updated test assertion from "0.20 * score_0" to "0.20 * @score_0"
to match the actual implementation required for proper FT.AGGREGATE execution.

Author: bsbodden

core/src/main/java/com/redis/vl/query/MultiVectorQuery.java

@@ -181,12 +181,13 @@ public Map<String, Object> getParams() {
    * Build the Redis AggregationBuilder for multi-vector search.
    *
    * <p>Creates an aggregation pipeline with:
+   *
    * <ul>
-   *   <li>LOAD all return fields</li>
-   *   <li>APPLY score calculations for each vector: score_i = (2 - distance_i) / 2</li>
-   *   <li>APPLY final combined score: w_1 * score_1 + w_2 * score_2 + ...</li>
-   *   <li>SORTBY combined_score DESC</li>
-   *   <li>LIMIT numResults</li>
+   *   <li>LOAD all return fields
+   *   <li>APPLY score calculations for each vector: score_i = (2 - distance_i) / 2
+   *   <li>APPLY final combined score: w_1 * score_1 + w_2 * score_2 + ...
+   *   <li>SORTBY combined_score DESC
+   *   <li>LIMIT numResults
    * </ul>
    *
    * @return Configured AggregationBuilder

core/src/test/java/com/redis/vl/query/MultiVectorQueryTest.java

@@ -289,8 +289,8 @@ void testMultiVectorQueryScoringFormula() {
 
     String formula = query.getScoringFormula();
 
-    // Expected: "0.20 * score_0 + 0.70 * score_1"
-    assertThat(formula).contains("0.20 * score_0").contains("0.70 * score_1").contains(" + ");
+    // Expected: "0.20 * @score_0 + 0.70 * @score_1" (@ prefix required for Redis aggregation)
+    assertThat(formula).contains("0.20 * @score_0").contains("0.70 * @score_1").contains(" + ");
   }
 
   @Test