sc-340182 - fix the report with new versions of Flask, fix the plugin…

[Gaubiche]

This PR fixes two bugs:

• crash when using a preprocessed set coming as a sparse matrix
• crash when using an algorithm with a code-env with flask 2.3+

[alexisdurieux]

This works fine :) If we want to be fully complete. I believe we could have a test case in test_tree_parser.py though. What do you think ?

[alexisdurieux]

http://dku54.dku.sh:15000/projects/PLUGINTESTMODELERRORANALYSIS/jobs/Scenario_build_output__NP__2026-09-16T09-49-57.416/
is good. ✅
This is unrelated to this PR so I don't think it should block the merge but there is an issue with the other:

[09:50:11] [INFO] [dku.utils]  - platform linux -- Python 3.9.25, pytest-8.4.2, pluggy-1.6.0 -- /data/home/dataiku/dss-home/backups_dataiku/copy_data_from_dss_14_to_dss15/code-envs/python/plugin_test_model_error_analysis/bin/python
[09:50:11] [INFO] [dku.utils]  - cachedir: .pytest_cache
[09:50:11] [INFO] [dku.utils]  - rootdir: /data/home/dataiku/dss-home/backups_dataiku/copy_data_from_dss_14_to_dss15/plugins/installed/model-error-analysis/resource/py
[09:50:11] [INFO] [dku.utils]  - configfile: pytest.ini
[09:50:11] [INFO] [dku.utils]  - plugins: allure-pytest-2.13.3, dataiku-plugin-tests-utils-0.0.1, mock-3.15.1
[09:50:12] [INFO] [dku.utils]  - collecting ... collected 0 items / 1 error
[09:50:12] [INFO] [dku.utils]  - ==================================== ERRORS ====================================
[09:50:12] [INFO] [dku.utils]  - ___________________ ERROR collecting test_dku_visualizer.py ____________________
[09:50:12] [INFO] [dku.utils]  - In test_plot_feature_distributions_no_show_global: function uses no fixture 'dss_target'

[Gaubiche]

Thanks for your review @alexisdurieux.

The tests are patched:

analysis/resource/py/test_dku_visualizer.py::test_failed_init[DSS13] PASSED [ 77%]
[12:14:19] [INFO] [dku.utils]  - ../../../../../../plugins/installed/model-error-analysis/resource/py/test_dku_visualizer.py::test_failed_init[DSS14] PASSED [ 88%]
[12:14:19] [INFO] [dku.utils]  - ../../../../../../plugins/installed/model-error-analysis/resource/py/test_dku_visualizer.py::test_failed_init[DSS15] PASSED [100%]

Merging