fix(python): use exact integer math for list_versions timestamps (#4426)

Refs #4404.

AsyncTable.list_versions split the nanosecond timestamp with float
division/modulo (`ts // 1e9`, `ts % 1e9`).
At ~1.8e18 a float can't hold every integer, so the microseconds drifted
(.274000 came back as .273999).

Use `divmod(ts, 1_000_000_000)` and integer // 1000 instead.

Only the precision fix is included here. Timezone-aware UTC (option 1 in
#4404) is on hold for now,
and I can add it here or in a follow-up depending on what they prefer.

Added test_list_versions_timestamp_precision using the value from the 
issue (1790989429274000000), expecting microsecond == 274000.

python/python/lancedb/table.py

@@ -6925,9 +6925,11 @@ class AsyncTable:
         """
         versions = await self._inner.list_versions()
         for v in versions:
-            ts_nanos = v["timestamp"]
-            v["timestamp"] = datetime.fromtimestamp(ts_nanos // 1e9) + timedelta(
-                microseconds=(ts_nanos % 1e9) // 1e3
+            # Use integer math: float division on ~1e18 nanosecond
+            # values loses sub-millisecond precision.
+            seconds, nanos = divmod(v["timestamp"], 1_000_000_000)
+            v["timestamp"] = datetime.fromtimestamp(seconds) + timedelta(
+                microseconds=nanos // 1000
             )
 
         return versions

python/python/tests/test_table.py

@@ -993,6 +993,63 @@ def test_polars(mem_db: DBConnection):
     assert len(filtered_result) == 2
 
 
+@pytest.mark.asyncio
+async def test_list_versions_timestamp_precision():
+    # 2026-10-03T01:03:49.274Z in nanoseconds. Float math turns .274000 into
+    # .273999, so make sure the conversion is exact.
+    ts_nanos = 1790989429274000000
+
+    class FakeInner:
+        async def list_versions(self):
+            return [{"version": 1, "timestamp": ts_nanos, "metadata": {}}]
+
+    table = table_module.AsyncTable(FakeInner())
+    versions = await table.list_versions()
+
+    expected = datetime.fromtimestamp(ts_nanos // 1_000_000_000)
+    assert versions[0]["timestamp"] == expected + timedelta(microseconds=274000)
+    assert versions[0]["timestamp"].microsecond == 274000
+
+
+def test_list_versions_timestamp_precision_sync(mem_db: DBConnection):
+    # The sync LanceTable.list_versions delegates to AsyncTable.list_versions,
+    # which is the path the parity report hit.
+    ts_nanos = 1790989429274000000
+
+    class FakeInner:
+        async def list_versions(self):
+            return [{"version": 1, "timestamp": ts_nanos, "metadata": {}}]
+
+    table = mem_db.create_table("ts_precision", data=[{"id": 1}])
+    table._table = table_module.AsyncTable(FakeInner())
+    versions = table.list_versions()
+
+    expected = datetime.fromtimestamp(ts_nanos // 1_000_000_000)
+    assert versions[0]["timestamp"] == expected + timedelta(microseconds=274000)
+    assert versions[0]["timestamp"].microsecond == 274000
+
+
+def test_list_versions_timestamp_precision_remote():
+    # RemoteTable.list_versions also delegates to AsyncTable.list_versions.
+    from lancedb.remote.table import RemoteTable
+
+    ts_nanos = 1790989429274000000
+
+    class FakeInner:
+        def name(self):
+            return "ts_precision"
+
+        async def list_versions(self):
+            return [{"version": 1, "timestamp": ts_nanos, "metadata": {}}]
+
+    table = RemoteTable(table_module.AsyncTable(FakeInner()), "dev")
+    versions = table.list_versions()
+
+    expected = datetime.fromtimestamp(ts_nanos // 1_000_000_000)
+    assert versions[0]["timestamp"] == expected + timedelta(microseconds=274000)
+    assert versions[0]["timestamp"].microsecond == 274000
+
+
 def test_versioning(mem_db: DBConnection):
     table = mem_db.create_table(
         "test",