Address deprecation warning

[bjlittle]

📰 Custom Issue

We need to address the following warning:

DeprecationWarning: `product` is deprecated as of NumPy 1.25.0, and will be removed in NumPy 2.0. Please use `prod` instead.

Which is generated in the tests.

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[HGWright]

I think that this was completed as part of #288. I cannot find any occurrences of product, it seems that they have all been replaced with prod already. The warning is also not raised in #310 or #292.