fix: parse RFC 3339 created_at and improve IndexConfig repr (#3558)

The server now serializes an index's `created_at` as an RFC 3339 string
(e.g. `"2026-06-18T21:37:36.637Z"`), but the client deserializer only
accepted a unix timestamp in milliseconds. This caused `list_indices` to
fail with:

```
Failed to parse list_indices response: invalid type: string "2026-06-18T21:37:36.637Z", expected a unix timestamp in milliseconds
```

This PR replaces the fixed millisecond deserializer with a custom one
that accepts both an RFC 3339 string (current server) and a
unix-millisecond integer (legacy deployments), so the client works
against any server version.

It also improves the `IndexConfig` repr in the Python bindings.
Previously it printed only three fields (`Index(FTS, columns=["text"],
name="text_idx")`), hiding the metadata that `list_indices` returns. It
now renders every populated field, omitting any that are `None`. Each
value is valid Python — integer counts use `_` thousands separators and
`created_at` uses the `datetime` repr — so values round-trip. The real
repr is a single line; it's wrapped here for readability:

```python
>>> table.list_indices()
[IndexConfig(
    name="text_idx",
    index_type="FTS",
    columns=["text"],
    index_uuid="aefd3e00-2f95-4bdc-92ac-06de84442bf1",
    type_url="/lance.table.InvertedIndexDetails",
    created_at=datetime.datetime(2026, 6, 18, 21, 37, 36, 637000, tzinfo=datetime.timezone.utc),
    num_indexed_rows=2,
    size_bytes=3_669,
    num_segments=1,
    index_version=1,
    index_details={
        'lance_tokenizer': None,
        'base_tokenizer': 'simple',
        'language': 'English',
        'with_position': False,
        'max_token_length': 40,
        'lower_case': True,
        'stem': True,
        'remove_stop_words': True,
        'custom_stop_words': None,
        'ascii_folding': True,
        'min_ngram_length': 3,
        'max_ngram_length': 3,
        'prefix_only': False,
    },
)]
```

Fixes #3556

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

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

python/python/tests/test_index.py

@@ -91,7 +91,9 @@ async def test_create_scalar_index(some_table: AsyncTable):
     # Can recreate if replace=True
     await some_table.create_index("id", replace=True)
     indices = await some_table.list_indices()
-    assert str(indices) == '[Index(BTree, columns=["id"], name="id_idx")]'
+    assert str(indices).startswith(
+        '[IndexConfig(name="id_idx", index_type="BTree", columns=["id"]'
+    )
     assert len(indices) == 1
     assert indices[0].index_type == "BTree"
     assert indices[0].columns == ["id"]
@@ -106,6 +108,27 @@ async def test_create_scalar_index(some_table: AsyncTable):
     assert len(indices) == 0
 
 
+@pytest.mark.asyncio
+async def test_index_config_repr(db_async):
+    # Use >= 1000 rows so the thousands separator in the repr is exercised.
+    nrows = 1500
+    table = await db_async.create_table(
+        "repr_table", pa.Table.from_pydict({"id": list(range(nrows))})
+    )
+    await table.create_index("id", config=BTree())
+    indices = await table.list_indices()
+    assert len(indices) == 1
+
+    r = repr(indices[0])
+    assert r.startswith('IndexConfig(name="id_idx", index_type="BTree", columns=["id"]')
+    # Integer counts use `_` thousands separators (valid Python int syntax).
+    assert "num_indexed_rows=1_500" in r
+    assert "num_unindexed_rows=0" in r
+    # created_at renders as a datetime so the value round-trips.
+    assert "created_at=datetime.datetime(" in r
+    assert r.endswith(")")
+
+
 @pytest.mark.asyncio
 async def test_create_nested_scalar_index_lists_canonical_paths(db_async):
     metadata_type = pa.struct(
@@ -198,7 +221,9 @@ async def test_create_nested_scalar_index_lists_canonical_paths(db_async):
 async def test_create_fixed_size_binary_index(some_table: AsyncTable):
     await some_table.create_index("fsb", config=BTree())
     indices = await some_table.list_indices()
-    assert str(indices) == '[Index(BTree, columns=["fsb"], name="fsb_idx")]'
+    assert str(indices).startswith(
+        '[IndexConfig(name="fsb_idx", index_type="BTree", columns=["fsb"]'
+    )
     assert len(indices) == 1
     assert indices[0].index_type == "BTree"
     assert indices[0].columns == ["fsb"]
@@ -247,7 +272,9 @@ async def test_create_bitmap_index(some_table: AsyncTable):
 async def test_create_label_list_index(some_table: AsyncTable):
     await some_table.create_index("tags", config=LabelList())
     indices = await some_table.list_indices()
-    assert str(indices) == '[Index(LabelList, columns=["tags"], name="tags_idx")]'
+    assert str(indices).startswith(
+        '[IndexConfig(name="tags_idx", index_type="LabelList", columns=["tags"]'
+    )
     plan = await some_table.query().where("array_has(tags, 'tag0')").explain_plan()
     assert "ScalarIndexQuery" in plan
 
@@ -262,7 +289,9 @@ async def test_create_large_list_label_list_index(db_async):
 
     await table.create_index("tags", config=LabelList())
     indices = await table.list_indices()
-    assert str(indices) == '[Index(LabelList, columns=["tags"], name="tags_idx")]'
+    assert str(indices).startswith(
+        '[IndexConfig(name="tags_idx", index_type="LabelList", columns=["tags"]'
+    )
     plan = await table.query().where("array_has(tags, 'shared')").explain_plan()
     assert "ScalarIndexQuery" in plan
 
@@ -299,7 +328,9 @@ async def test_create_label_list_index_rejects_list_struct(db_async):
 async def test_full_text_search_index(some_table: AsyncTable):
     await some_table.create_index("tags", config=FTS(with_position=False))
     indices = await some_table.list_indices()
-    assert str(indices) == '[Index(FTS, columns=["tags"], name="tags_idx")]'
+    assert str(indices).startswith(
+        '[IndexConfig(name="tags_idx", index_type="FTS", columns=["tags"]'
+    )
 
     await some_table.prewarm_index("tags_idx")