Change to scikit-learn tree node type breaks `treelite.sklearn.export_model`

[betatim]

scikit-learn 1.10.0.dev0 (the nightly version of scikit-learn) uses a different node type to 1.9.0.

For example in cuml's nightly we get failures related to this https://github.com/NVIDIA/cuml/actions/runs/33059973711/job/98476087166

I've picked out one test failure and put it in the detail below. The test itself is integration/test_rf_classifier.py::test_oob_score

A minimal reproducer with the nightly version of scikit-learn:

import sklearn
import treelite.sklearn
from sklearn.datasets import make_classification
from sklearn.ensemble import RandomForestClassifier

print(f"sklearn={sklearn.__version__} treelite={treelite.__version__}")

X, y = make_classification(n_samples=100, n_features=4, random_state=0)
model = RandomForestClassifier(n_estimators=2, max_depth=3).fit(X, y)

tl_model = treelite.sklearn.import_model(model)
treelite.sklearn.export_model(tl_model)

scikit-learn/scikit-learn#33972 is the PR that made the relevant change.

Full test failure

________________________________ test_oob_score ________________________________
[gw1] linux -- Python 3.14.7 /pyenv/versions/3.14.7/bin/python
Traceback (most recent call last):
  File "/pyenv/versions/3.14.7/lib/python3.14/site-packages/_pytest/runner.py", line 361, in from_call
    result: TResult | None = func()
                             ~~~~^^
  File "/pyenv/versions/3.14.7/lib/python3.14/site-packages/_pytest/runner.py", line 250, in <lambda>
    lambda: runtest_hook(item=item, **kwds),
            ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^
  File "/pyenv/versions/3.14.7/lib/python3.14/site-packages/pluggy/_hooks.py", line 512, in __call__
    return self._hookexec(self.name, self._hookimpls.copy(), kwargs, firstresult)
           ~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/pyenv/versions/3.14.7/lib/python3.14/site-packages/pluggy/_manager.py", line 120, in _hookexec
    return self._inner_hookexec(hook_name, methods, kwargs, firstresult)
           ~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/pyenv/versions/3.14.7/lib/python3.14/site-packages/pluggy/_callers.py", line 167, in _multicall
    raise exception
  File "/pyenv/versions/3.14.7/lib/python3.14/site-packages/pluggy/_callers.py", line 139, in _multicall
    teardown.throw(exception)
    ~~~~~~~~~~~~~~^^^^^^^^^^^
  File "/pyenv/versions/3.14.7/lib/python3.14/site-packages/_pytest/logging.py", line 865, in pytest_runtest_call
    yield
  File "/pyenv/versions/3.14.7/lib/python3.14/site-packages/pluggy/_callers.py", line 139, in _multicall
    teardown.throw(exception)
    ~~~~~~~~~~~~~~^^^^^^^^^^^
  File "/pyenv/versions/3.14.7/lib/python3.14/site-packages/_pytest/capture.py", line 900, in pytest_runtest_call
    return (yield)
            ^^^^^
  File "/pyenv/versions/3.14.7/lib/python3.14/site-packages/pluggy/_callers.py", line 139, in _multicall
    teardown.throw(exception)
    ~~~~~~~~~~~~~~^^^^^^^^^^^
  File "/pyenv/versions/3.14.7/lib/python3.14/site-packages/pluggy/_callers.py", line 53, in run_old_style_hookwrapper
    return result.get_result()
           ~~~~~~~~~~~~~~~~~^^
  File "/pyenv/versions/3.14.7/lib/python3.14/site-packages/pluggy/_result.py", line 103, in get_result
    raise exc.with_traceback(tb)
  File "/pyenv/versions/3.14.7/lib/python3.14/site-packages/pluggy/_callers.py", line 38, in run_old_style_hookwrapper
    res = yield
          ^^^^^
  File "/pyenv/versions/3.14.7/lib/python3.14/site-packages/pluggy/_callers.py", line 139, in _multicall
    teardown.throw(exception)
    ~~~~~~~~~~~~~~^^^^^^^^^^^
  File "/pyenv/versions/3.14.7/lib/python3.14/site-packages/_pytest/skipping.py", line 268, in pytest_runtest_call
    return (yield)
            ^^^^^
  File "/pyenv/versions/3.14.7/lib/python3.14/site-packages/pluggy/_callers.py", line 121, in _multicall
    res = hook_impl.function(*args)
  File "/pyenv/versions/3.14.7/lib/python3.14/site-packages/_pytest/runner.py", line 184, in pytest_runtest_call
    item.runtest()
    ~~~~~~~~~~~~^^
  File "/pyenv/versions/3.14.7/lib/python3.14/site-packages/_pytest/python.py", line 1707, in runtest
    self.ihook.pytest_pyfunc_call(pyfuncitem=self)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
  File "/pyenv/versions/3.14.7/lib/python3.14/site-packages/pluggy/_hooks.py", line 512, in __call__
    return self._hookexec(self.name, self._hookimpls.copy(), kwargs, firstresult)
           ~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/pyenv/versions/3.14.7/lib/python3.14/site-packages/pluggy/_manager.py", line 120, in _hookexec
    return self._inner_hookexec(hook_name, methods, kwargs, firstresult)
           ~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/pyenv/versions/3.14.7/lib/python3.14/site-packages/pluggy/_callers.py", line 167, in _multicall
    raise exception
  File "/pyenv/versions/3.14.7/lib/python3.14/site-packages/pluggy/_callers.py", line 121, in _multicall
    res = hook_impl.function(*args)
  File "/pyenv/versions/3.14.7/lib/python3.14/site-packages/_pytest/python.py", line 167, in pytest_pyfunc_call
    result = testfunction(**testargs)
  File "/__w/cuml/cuml/python/cuml/cuml_accel_tests/integration/test_rf_classifier.py", line 238, in test_oob_score
    assert isinstance(clf.oob_score_, float)
                      ^^^^^^^^^^^^^^
  File "/pyenv/versions/3.14.7/lib/python3.14/site-packages/cuml/accel/estimator_proxy.py", line 587, in __getattr__
    self._sync_attrs_to_cpu()
    ~~~~~~~~~~~~~~~~~~~~~~~^^
  File "/pyenv/versions/3.14.7/lib/python3.14/site-packages/cuml/accel/estimator_proxy.py", line 333, in _sync_attrs_to_cpu
    self._gpu._sync_attrs_to_cpu(self._cpu)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^
  File "/pyenv/versions/3.14.7/lib/python3.14/site-packages/cuml/internals/outputs.py", line 818, in inner
    res = func(*args, **kwargs)
  File "/pyenv/versions/3.14.7/lib/python3.14/site-packages/cuml/internals/interop.py", line 185, in _sync_attrs_to_cpu
    attrs = self._attrs_to_cpu(model)
  File "/pyenv/versions/3.14.7/lib/python3.14/site-packages/cuml/ensemble/randomforestclassifier.py", line 196, in _attrs_to_cpu
    attrs = super()._attrs_to_cpu(model)
  File "cuml/ensemble/randomforest_common.pyx", line 288, in cuml.ensemble.randomforest_common.BaseRandomForestModel._attrs_to_cpu
    sk_model = treelite.sklearn.export_model(tl_model)
    ^^^
  File "/pyenv/versions/3.14.7/lib/python3.14/site-packages/treelite/sklearn/exporter.py", line 236, in export_model
    _export_tree(
    ~~~~~~~~~~~~^
        model,
        ^^^^^^
    ...<5 lines>...
        subestimator_class=subestimator_class,
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
  File "/pyenv/versions/3.14.7/lib/python3.14/site-packages/treelite/sklearn/exporter.py", line 133, in _export_tree
    tree.__setstate__(state)
    ~~~~~~~~~~~~~~~~~^^^^^^^
  File "sklearn/tree/_tree.pyx", line 896, in sklearn.tree._tree.Tree.__setstate__
  File "sklearn/tree/_tree.pyx", line 1655, in sklearn.tree._tree._check_node_ndarray
    raise ValueError(
ValueError: node array from the pickle has an incompatible dtype:
- expected: {'names': ['left_child', 'right_child', 'feature', 'threshold', 'left_cat_bitset', 'impurity', 'n_node_samples', 'weighted_n_node_samples', 'missing_go_to_left', 'split_kind'], 'formats': ['<i8', '<i8', '<i8', '<f8', ('<u4', (8,)), '<f8', '<i8', '<f8', 'u1', 'i1'], 'offsets': [0, 8, 16, 24, 32, 64, 72, 80, 88, 89], 'itemsize': 96, 'aligned': True}
- got     : {'names': ['left_child', 'right_child', 'feature', 'threshold', 'left_cat_bitset', 'impurity', 'n_node_samples', 'weighted_n_node_samples', 'missing_go_to_left'], 'formats': ['<i8', '<i8', '<i8', '<f8', ('<u4', (8,)), '<f8', '<i8', '<f8', 'u1'], 'offsets': [0, 8, 16, 24, 32, 64, 72, 80, 88], 'itemsize': 96, 'aligned': True}