Update sklearn exporter for scikit-learn 1.10+

[chyunsu3]

Closes #674

I validated the changes by running

pytest -vx -rxXs tests/python/test_sklearn_integration.py::test_skl_export_rf_regressor

with both scikit-learn 1.9 and 1.10 (nightly).

cc @betatim

[codecov]

Codecov Report

❌ Patch coverage is 70.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.90%. Comparing base (96cb305) to head (45fcf67).

Files with missing lines	Patch %	Lines
python/treelite/sklearn/exporter.py	70.00%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           mainline     #675      +/-   ##
============================================
- Coverage     83.93%   83.90%   -0.03%     
============================================
  Files            75       75              
  Lines          6816     6823       +7     
  Branches        557      557              
============================================
+ Hits           5721     5725       +4     
- Misses         1095     1098       +3     

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[betatim]

I don't really know the treelite code base so I can't really review this, but it looks reasonable to have a version dependent branch.

Do you want to add a regression test to this?

[chyunsu3]

Do you want to add a regression test to this?

We already have tests/python/test_sklearn_integration.py::test_skl_export_rf_regressor. To check regressions, we'd need to test a nightly version of scikit-learn in the Treelite CI. I opened #677 to follow up.