Change VectorReaderListener to expect number array (opensearch-projec…

…t#416)

Refactors VectorReaderListener onResponse to expect arrays of Number
type from search result instead of Double type. Adds test case to
confirm that it can handle Integer type. Cleans up tests in
VectorReaderTest class.

Signed-off-by: John Mazanec <jmazane@amazon.com>

src/main/java/org/opensearch/knn/training/VectorReader.java

@@ -184,7 +184,7 @@ public void onResponse(SearchResponse searchResponse) {
 
             for (int i = 0; i < vectorsToAdd; i++) {
                 trainingData.add(
-                    ((List<Double>) hits[i].getSourceAsMap().get(fieldName)).stream().map(Double::floatValue).toArray(Float[]::new)
+                    ((List<Number>) hits[i].getSourceAsMap().get(fieldName)).stream().map(Number::floatValue).toArray(Float[]::new)
                 );
             }