feat(bindings): expose new IndexConfig fields in Python and Node.js (#3534)

## Summary

Surfaces the rich per-index metadata added in #3497 to the Python and
Node.js language bindings. Closes #3495.

New optional fields exposed on `IndexConfig` in both bindings:

- `index_uuid` / `indexUuid` — UUID of the first index segment
- `type_url` / `typeUrl` — protobuf type URL for the index
- `created_at` / `createdAt` — creation timestamp (milliseconds since
Unix epoch)
- `num_indexed_rows` / `numIndexedRows` — rows covered by the index
- `num_unindexed_rows` / `numUnindexedRows` — rows not yet indexed
- `size_bytes` / `sizeBytes` — total index file size in bytes
- `num_segments` / `numSegments` — number of index segments
- `index_version` / `indexVersion` — on-disk format version
- `index_details` / `indexDetails` — type-specific JSON details string

All fields are `None`/`undefined` for remote tables (which don't yet
surface this metadata through the server response).

## Changes

- `python/src/index.rs`: extend `IndexConfig` pyclass; update `From`
impl; update `__getitem__`
- `python/python/lancedb/_lancedb.pyi`: add type hints for new fields
- `python/python/tests/test_table.py`: new `test_index_config_fields`
test
- `nodejs/src/table.rs`: extend `IndexConfig` napi struct; update `From`
impl
- `nodejs/__test__/table.test.ts`: new test; update existing `toEqual`
assertions to `expect.objectContaining` to accommodate new fields

## Test plan

- [x] Python: `uv run --extra tests pytest
python/tests/test_table.py::test_index_config_fields`
- [x] Node.js: `pnpm test __test__/table.test.ts`

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

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/src/js/interfaces/IndexConfig.md

@@ -23,6 +23,31 @@ be more columns to represent composite indices.
 
 ***
 
+### createdAt?
+
+```ts
+optional createdAt: Date;
+```
+
+When the index was created.
+
+`undefined` for remote tables or indices created before timestamps were tracked.
+
+***
+
+### indexDetails?
+
+```ts
+optional indexDetails: any;
+```
+
+Index-type-specific details parsed as a JavaScript object.
+
+Falls back to a raw string if JSON parsing fails. `undefined` for
+remote tables or when details are unavailable.
+
+***
+
 ### indexType
 
 ```ts
@@ -33,6 +58,30 @@ The type of the index
 
 ***
 
+### indexUuid?
+
+```ts
+optional indexUuid: string;
+```
+
+The UUID of the first segment of the index.
+
+`undefined` for remote tables, which do not yet surface this.
+
+***
+
+### indexVersion?
+
+```ts
+optional indexVersion: number;
+```
+
+The on-disk index format version.
+
+`undefined` for remote tables.
+
+***
+
 ### name
 
 ```ts
@@ -40,3 +89,63 @@ name: string;
 ```
 
 The name of the index
+
+***
+
+### numIndexedRows?
+
+```ts
+optional numIndexedRows: number;
+```
+
+The number of rows indexed, across all segments.
+
+`undefined` for remote tables.
+
+***
+
+### numSegments?
+
+```ts
+optional numSegments: number;
+```
+
+The number of segments that make up the index.
+
+`undefined` for remote tables.
+
+***
+
+### numUnindexedRows?
+
+```ts
+optional numUnindexedRows: number;
+```
+
+The number of rows not yet covered by this index.
+
+`undefined` for remote tables.
+
+***
+
+### sizeBytes?
+
+```ts
+optional sizeBytes: number;
+```
+
+The total size in bytes of all index files across all segments.
+
+`undefined` for remote tables or indices without size tracking.
+
+***
+
+### typeUrl?
+
+```ts
+optional typeUrl: string;
+```
+
+The protobuf type URL, a precise type identifier for the index.
+
+`undefined` for remote tables.