1444: Added alternative argument to test_proportion_diff()

[danielinteractive]

part of #1444

Also:

• adds air.toml excluding the whole project from auto formatting when Air is used by developer
• Updates my email address

[github-actions]

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[danielinteractive]

I have read the CLA Document and I hereby sign the CLA

[Melkiades]

It looks very very good!! Thanks @danielinteractive, it is practically ready. Only .gitignore, a couple of extra spaces, and the snapshots and it is good to go

[danielinteractive]

Thanks @Melkiades for your swift review, Air config files have been removed and the GHA checks are green now 👍

[Melkiades]

Lgtm! Thanks Daniel for the addition. Very clear code ;)

[danielinteractive]

Thanks @Melkiades , feel free to merge, I can't somehow 😄