feat(fts): support custom stop-word lists (#3734)

## What

Expose custom FTS stop-word lists in the Python and TypeScript public
APIs, including their standalone tokenize helpers and remote index
creation.

This PR supports concrete string lists only. It does not add file or
LanceDB-table stop-word sources.

## Why

Rust already exposes Lance's custom stop-word list option. The Python
and TypeScript APIs did not pass it through, and local index details did
not retain the full tokenizer parameters needed by index-backed
tokenization after reopening a table.

## How

- Add `custom_stop_words` / `customStopWords` to the Python and
TypeScript FTS and tokenize options.
- Preserve `None` / `undefined`, empty lists, and list contents without
normalization.
- Load the persisted FTS segment parameters when returning local index
details.
- Serialize the concrete list in remote create-index requests.
- Keep Python and TypeScript tests thin; behavior, persistence, query
tokenization, and remote JSON coverage live primarily in Rust.

## Validation

- `cargo check --quiet --features remote --tests --examples`
- `cargo clippy --quiet --features remote --tests --examples`
- `cargo test --quiet --features remote --tests`
- Python extension rebuild with `uv` and `maturin`
- Targeted Python tests: 4 passed
- Python `ruff format --check` and `ruff check`
- TypeScript build, typecheck, Biome lint, generated docs, and targeted
tests

---------

Co-authored-by: Yang Cen <yangcen@Yangs-Mac-mini.local>

python/python/tests/test_fts.py

@@ -219,11 +219,13 @@ def test_create_inverted_index(table, with_position):
         table.create_fts_index(
             "text",
             with_position=with_position,
+            custom_stop_words=["puppy"],
             name="custom_fts_index",
         )
     indices = table.list_indices()
     fts_indices = [i for i in indices if i.index_type == "FTS"]
     assert any(i.name == "custom_fts_index" for i in fts_indices)
+    assert fts_indices[0].index_details["custom_stop_words"] == ["puppy"]
 
 
 @pytest.mark.parametrize("block_size", [128, 256])
@@ -243,6 +245,24 @@ def test_create_inverted_index_rejects_invalid_block_size(table):
         table.create_index("text", config=FTS(block_size=129))
 
 
+def test_custom_stop_words_list(table):
+    table.create_index(
+        "text",
+        config=FTS(stem=False, custom_stop_words=["lance"]),
+    )
+
+    assert table.list_indices()[0].index_details["custom_stop_words"] == ["lance"]
+    tokens = table.tokenize("the lance data", column="text")
+    assert [token.text for token in tokens] == ["the", "data"]
+    empty_tokens = ldb.tokenize("the lance data", stem=False, custom_stop_words=[])
+    assert [token.text for token in empty_tokens] == ["the", "lance", "data"]
+    with pytest.raises(TypeError, match=r"custom_stop_words.*int"):
+        ldb.tokenize(
+            "the lance data",
+            custom_stop_words=["lance", 42],
+        )
+
+
 def test_search_fts(table):
     table.create_fts_index("text")
     results = table.search("puppy").select(["id", "text"]).limit(5).to_list()

python/python/tests/test_remote_db.py

@@ -771,6 +771,7 @@ def test_table_create_indices():
                 "text",
                 wait_timeout=timedelta(seconds=2),
                 block_size=256,
+                custom_stop_words=["cloud"],
                 name="custom_fts_idx",
             )
 
@@ -795,6 +796,7 @@ def test_table_create_indices():
         assert "name" in fts_req
         assert fts_req["name"] == "custom_fts_idx"
         assert fts_req["block_size"] == 256
+        assert fts_req["custom_stop_words"] == ["cloud"]
 
         # Check vector index request has custom name
         vector_req = received_requests[2]