feat: add support for returning all scores with rerankers (#2509)

Previously `return_score="all"` was supported only for the default
reranker (RRF) and not the model based rerankers.
This adds support for keeping all scores in the base reranker so that
all model based rerankers can use it. Its a slower path than keeping
just the relevance score but can be useful in debugging

python/python/tests/test_rerankers.py

@@ -499,3 +499,19 @@ def test_empty_result_reranker():
             .rerank(reranker)
             .to_arrow()
         )
+
+
+@pytest.mark.parametrize("use_tantivy", [True, False])
+def test_cross_encoder_reranker_return_all(tmp_path, use_tantivy):
+    pytest.importorskip("sentence_transformers")
+    reranker = CrossEncoderReranker(return_score="all")
+    table, schema = get_test_table(tmp_path, use_tantivy)
+    query = "single player experience"
+    result = (
+        table.search(query, query_type="hybrid", vector_column_name="vector")
+        .rerank(reranker=reranker)
+        .to_arrow()
+    )
+    assert "_relevance_score" in result.column_names
+    assert "_score" in result.column_names
+    assert "_distance" in result.column_names