Add statistic product

[AdRiley]

Pull Request Description

Add Statistic.Product

Important Notes

Checklist

Please ensure that the following checklist has been satisfied before submitting the PR:

• The documentation has been updated, if necessary.
• Screenshots/screencasts have been attached, if there are any visual changes. For interactive or animated visual changes, a screencast is preferred.
• All code follows the
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  and
  Rust
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• Unit tests have been written where possible.

[radeusgd]

Looks good.

I'm not sure about the choice of the empty case. IMHO it makes sense to use 1 there, as then we get a property that
(a+b).compute Statistic.Product == (a.compute Statistic.Product) * (b.compute Statistic.Product), although I guess there is some rationale for 0 as a generic 'none'. But then I guess Nothing would also be valid?