[ENH] issues and features for the Empirical distribution

[smilingprogrammer]

Reference Issues/PRs

Fix for #283

What does this implement/fix? Explain your changes.

• Empirical.sample now honors time_indep: scalar distributions still delegate to the base implementation, but multidimensional ones keep entire time series intact when time_indep=False and behave exactly as before when True.
• Added a row_indep flag (default True) so users can couple or decouple rows independently of the time axis; adaptered it also to QPD_Empirical

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

No

What should a reviewer concentrate their feedback on?

correctness of implementation

Did you add any tests for the change?

Not yet. Need initial review before proceeding to add a test.

Any other comments?

This is an initial fix towards resolving issue #283. After initial review, we can proceed to re-iterate for improvement and add a test.

PR checklist

For all contributions

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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.
• I've added one or more illustrative usage examples to the docstring, in a pydocstyle compliant Examples section.
• If the estimator relies on a soft dependency, I've set the python_dependencies tag and ensured
  dependency isolation, see the estimator dependencies guide.