fix: *sklearn* version compability in stacking_cv params

[d-kleine]

Description

Enhances compatibility with scikit-learn versions 1.4 and above by adjusting parameter handling in the stacking_cv functions (classification, regression)

tests:
pytest ./mlxtend/classifier/tests/test_stacking_cv_classifier.py -sv
pytest ./mlxtend/regressor/tests/test_stacking_cv_regression.py -sv

Related issues or pull requests

fixes #1117

Pull Request Checklist

• Added a note about the modification or contribution to the ./docs/sources/CHANGELOG.md file (if applicable)
• Added appropriate unit test functions in the ./mlxtend/*/tests directories (if applicable)
• Modify documentation in the corresponding Jupyter Notebook under mlxtend/docs/sources/ (if applicable)
• Ran PYTHONPATH='.' pytest ./mlxtend -sv and make sure that all unit tests pass (for small modifications, it might be sufficient to only run the specific test file, e.g., PYTHONPATH='.' pytest ./mlxtend/classifier/tests/test_stacking_cv_classifier.py -sv)
• Checked for style issues by running flake8 ./mlxtend

[rasbt]

I completely missed this earlier, thanks for the fix!

[rasbt]

Looks great! Also thanks for adding that toggle for backward compatibility!