fix(tasks): infer task_type string from TaskType in create_task

[shellyco-code]

Metadata

• Reference Issue: Fixes [BUG] create_task() hardcodes task_type="None" instead of inferring type string from TaskType #1766
• New Tests Added: Yes
• Documentation Updated: Yes
• Change Log Entry: "Fix create_task() hardcoding task_type as string 'None' by adding type_str property to TaskType"

Details

• What does this PR implement/fix?

  • Adds @property def type_str(self) -> str to TaskType mapping each enum member to its canonical OpenML string name (e.g., "Supervised Classification", "Supervised Regression", "Clustering", "Learning Curve", etc.).
  • Resolves # TODO: refactor to get task type string from ID. in openml/tasks/functions.py:create_task by passing task_type=task_type.type_str to task_cls.
  • Ensures OpenMLTask.__init__ defaults self.task_type = task_type if task_type is not None else task_type_id.type_str.
  • Adds offline unit tests test_create_task_sets_task_type() and test_task_type_str() in tests/test_tasks/test_task_functions.py.

• Why is this change necessary?
  Previously, any task created via create_task() received task_type="None" as a literal string. This caused checks like task.task_type == "Supervised Classification" to fail and resulted in representations and error messages outputting 'None'.

• How can I reproduce the issue this PR is solving and its solution?
  Run pytest tests/test_tasks/test_task_functions.py -k "test_create_task_sets_task_type or test_task_type_str". Both tests pass offline in < 0.2s.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.34%. Comparing base (4a25027) to head (9e3388b).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1767      +/-   ##
==========================================
- Coverage   81.50%   81.34%   -0.16%     
==========================================
  Files          63       63              
  Lines        5238     5242       +4     
==========================================
- Hits         4269     4264       -5     
- Misses        969      978       +9     

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