Promote array utils package

[z3dev]

These changes promote array-utils to a general package. The coalease() function from modeling has been added, as well as tested.

These are in preparation to using array-utils as a dependency in modeling, i.e. drop duplicate functions in modeling.

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[platypii]

The changes seem fine, but I don't love the idea of adding a dependency to modeling package. Right now it has zero dependencies which is pretty nice?

[z3dev]

The changes seem fine, but I don't love the idea of adding a dependency to modeling package. Right now it has zero dependencies which is pretty nice?

Tis nice. But the duplicate functions are kind of lame. The array-util functions can also be exported as part of the modeling API as well.

Anyway, this dependency can be added anytime.

Now, I just want to make this package (array-utils) into one of the major packages, rather than hiding under utils.