feat: add name parameter to remaining Python create index calls (#2617)

## Summary
This PR adds the missing `name` parameter to `create_scalar_index` and
`create_fts_index` methods in the Python SDK, which was inadvertently
omitted when it was added to `create_index` in PR #2586.

## Changes
- Add `name: Optional[str] = None` parameter to abstract
`Table.create_scalar_index` and `Table.create_fts_index` methods
- Update `LanceTable` implementation to accept and pass the `name`
parameter to the underlying Rust layer
- Update `RemoteTable` implementation to accept and pass the `name`
parameter
- Enhanced tests to verify custom index names work correctly for both
scalar and FTS indices
- When `name` is not provided, default names are generated (e.g.,
`{column}_idx`)

## Test plan
- [x] Added test cases for custom names in scalar index creation
- [x] Added test cases for custom names in FTS index creation  
- [x] Verified existing tests continue to pass
- [x] Code formatting and linting checks pass

This ensures API consistency across all index creation methods in the
LanceDB Python SDK.

Fixes #2616

🤖 Generated with [Claude Code](https://claude.ai/code)

---------

Co-authored-by: Claude <noreply@anthropic.com>

python/python/tests/test_table.py

@@ -1274,11 +1274,13 @@ def test_create_scalar_index(mem_db: DBConnection):
         "my_table",
         data=test_data,
     )
+    # Test with default name
     table.create_scalar_index("x")
     indices = table.list_indices()
     assert len(indices) == 1
     scalar_index = indices[0]
     assert scalar_index.index_type == "BTree"
+    assert scalar_index.name == "x_idx"  # Default name
 
     # Confirm that prefiltering still works with the scalar index column
     results = table.search().where("x = 'c'").to_arrow()
@@ -1292,6 +1294,14 @@ def test_create_scalar_index(mem_db: DBConnection):
     indices = table.list_indices()
     assert len(indices) == 0
 
+    # Test with custom name
+    table.create_scalar_index("y", name="custom_y_index")
+    indices = table.list_indices()
+    assert len(indices) == 1
+    scalar_index = indices[0]
+    assert scalar_index.index_type == "BTree"
+    assert scalar_index.name == "custom_y_index"
+
 
 def test_empty_query(mem_db: DBConnection):
     table = mem_db.create_table(