[ENH] Chi-Squared Distribution

[sukjingitsit]

Reference Issues/PRs

Addresses #22 for chi-squared case

What does this implement/fix? Explain your changes.

Implements some methods for chi-squared distribution

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

No

What should a reviewer concentrate their feedback on?

Current state of code, and what all capabilities need to be modified / made better (particularly, I am trying to implement energy and make ppf more native than a scipy wrapper)

Did you add any tests for the change?

Nope

Any other comments?

PR checklist

For all contributions

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• [Yes ] 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.

Thanks for contributing!
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[fkiraly]

Nice contribution!

Code formatting checks are failing, see here for a guide how to set this up locally:
https://www.sktime.net/en/stable/developer_guide/coding_standards.html

For the energy, let me know if you need help. Does the reference from the issue not have an explicit formula?

[sukjingitsit]

I do not understand what the build issue is, as it doesn't seem to show the files I modified, rather some other files

[fkiraly]

note sure, I've restarted the tests - let's see.

[fkiraly]

failures seem genuine - methods return unexpected values. Have you run check_estimator on the distribution?

[fkiraly]

Thanks. Updated with new extension contract.