feat: add finite() method to test entities for finiteness

[gwhitney]

Here's a version of the finite test called finite(), with matrices/arrays returning boolean as to whether all entries are finite.

If you want to change either the name or the behavior on arrays/matrices, let me know.

Resolves #3553.

[josdejong]

Thanks @gwhitney , this PR looks well taken care of! I'm a bit surprised we don't yet have a function to test finiteness 😅.

I made a couple of inline comments, can you have a look at those?

[gwhitney]

OK, I think that's everything you requested.

[josdejong]

Thanks a lot Glen!