feat: allow setting train=False and name on indices (#2586)

Enables two new parameters when building indices:

* `name`: Allows explicitly setting a name on the index. Default is
`{col_name}_idx`.
* `train` (default `True`): When set to `False`, an empty index will be
immediately created.

The upgrade of Lance means there are also additional behaviors from
cd76a993b8:

* When a scalar index is created on a Table, it will be kept around even
if all rows are deleted or updated.
* Scalar indices can be created on empty tables. They will default to
`train=False` if the table is empty.

---------

Co-authored-by: Weston Pace <weston.pace@gmail.com>

python/python/tests/test_table.py

@@ -670,7 +670,9 @@ def test_create_index_method(mock_create_index, mem_db: DBConnection):
         num_sub_vectors=96,
         num_bits=4,
     )
-    mock_create_index.assert_called_with("vector", replace=True, config=expected_config)
+    mock_create_index.assert_called_with(
+        "vector", replace=True, config=expected_config, name=None, train=True
+    )
 
     table.create_index(
         vector_column_name="my_vector",
@@ -680,7 +682,7 @@ def test_create_index_method(mock_create_index, mem_db: DBConnection):
     )
     expected_config = HnswPq(distance_type="dot")
     mock_create_index.assert_called_with(
-        "my_vector", replace=False, config=expected_config
+        "my_vector", replace=False, config=expected_config, name=None, train=True
     )
 
     table.create_index(
@@ -695,7 +697,44 @@ def test_create_index_method(mock_create_index, mem_db: DBConnection):
         distance_type="cosine", sample_rate=0.1, m=29, ef_construction=10
     )
     mock_create_index.assert_called_with(
-        "my_vector", replace=True, config=expected_config
+        "my_vector", replace=True, config=expected_config, name=None, train=True
+    )
+
+
+@patch("lancedb.table.AsyncTable.create_index")
+def test_create_index_name_and_train_parameters(
+    mock_create_index, mem_db: DBConnection
+):
+    """Test that name and train parameters are passed correctly to AsyncTable"""
+    table = mem_db.create_table(
+        "test",
+        data=[
+            {"vector": [3.1, 4.1], "id": 1},
+            {"vector": [5.9, 26.5], "id": 2},
+        ],
+    )
+
+    # Test with custom name
+    table.create_index(vector_column_name="vector", name="my_custom_index")
+    expected_config = IvfPq()  # Default config
+    mock_create_index.assert_called_with(
+        "vector",
+        replace=True,
+        config=expected_config,
+        name="my_custom_index",
+        train=True,
+    )
+
+    # Test with train=False
+    table.create_index(vector_column_name="vector", train=False)
+    mock_create_index.assert_called_with(
+        "vector", replace=True, config=expected_config, name=None, train=False
+    )
+
+    # Test with both name and train
+    table.create_index(vector_column_name="vector", name="my_index_name", train=True)
+    mock_create_index.assert_called_with(
+        "vector", replace=True, config=expected_config, name="my_index_name", train=True
     )