[ENH] Refactor of BaseDistribution and descendants - generalised distribution param broadcasting in base class

[Alex-JG3]

Reference Issues/PRs

Related issue sktime/skpro#21

What does this implement/fix? Explain your changes.

Moves the _get_bc_params method from child distributions to the parent distribtion class, BaseDistribution.

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

No

What should a reviewer concentrate their feedback on?

This implementation is quite simple and doesn't use _tags and still means the child distributions have to call the _get_bc_params method.

Would you prefer the child distributions to not have to call the _get_bc_params method. This will mean putting the parameter names that need to broadcasted in _tags dictionary then writing the broadcasted parameters from BaseDistribution. Personally I think this is slightly over complicated although this approach follows the DRY principles more closely. I am open to intput here and happy to implement whatever is preferred.

Did you add any tests for the change?

Altered the _DistrDefaultMethodTester class to use the parent _get_bc_params method.

Any other comments?

PR checklist

For all contributions

• I've added myself to the list of contributors with any new badges I've earned :-)
  How to: add yourself to the all-contributors file in the sktime root directory (not the CONTRIBUTORS.md). Common badges: code - fixing a bug, or adding code logic. doc - writing or improving documentation or docstrings. bug - reporting or diagnosing a bug (get this plus code if you also fixed the bug in the PR).maintenance - CI, test framework, release.
  See here for full badge reference
• Optionally, I've added myself and possibly others to the CODEOWNERS file - do this if you want to become the owner or maintainer of an estimator you added.
  See here for further details on the algorithm maintainer role.
• 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.

[fkiraly]

Hm, looks like an impovement!

Left some non-blocking suggestions.

Also, we should see if the tests run - as said, the skpro tests are more extensive, so let's open a copy there if this runs through.

[fkiraly]

Excellent, thanks! This will help greatly with the base class refactor.