[BUG] burr iii implementation was using the wrong scipy method

[hrshx3o5o6]

Reference Issues/PRs

Fixes #952

What does this implement/fix? Explain your changes.

This PR fixes a critical bug in the BurrIII distribution class where it incorrectly wrapped scipy.stats.burr12 (Burr Type XII) instead of scipy.stats.burr (Burr Type III).

Changes made:

• Updated BurrIII._get_scipy_object to return scipy.stats.burr.
• Updated BurrIII to correctly accept both the c and d shape parameters (previously, d was hardcoded to 1).
• Updated the math docstring and parameter descriptions to reflect the two shape parameters.
• Expanded get_test_params to thoroughly test cases where d != 1.0.

Does your contribution introduce a new dependency? If yes, which one?

No new dependencies.

What should a reviewer concentrate their feedback on?

• Correctness of the mathematical documentation in the docstring.
• Confirming that scipy.stats.burr behaves as expected with the new c, d, and scale mapping logic.

Did you add any tests for the change?

Yes, the existing generic test suite test_all_distrs.py thoroughly verifies the new parameters generated by the updated get_test_params class method.

Any other comments?

N/A

PR checklist

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• The PR title starts with either [ENH], [MNT], [DOC], or [BUG]. [BUG] - bugfix, [MNT] - CI, test framework, [ENH] - adding or improving code, [DOC] - writing or improving documentation or docstrings.

For new estimators

• I've added the estimator to the API reference - in docs/source/api_reference/taskname.rst, follow the pattern.
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[fkiraly]

Thanks!

By accident, this Pr seems to contain another one with unrelated content - can you please fix that?

[hrshx3o5o6]

Thanks for flagging that! I've cleaned up the branch now so it contains the BurrIII fix alone and have requested for review.