Add Least Common Multiple

This is an enhancement request to add least common multiple to the package. A major issue with least common multiple is that it is not uncommon for it to overflow when used with fixed width integers. This PR offers two functions, one that traps and one that throws should the result not be representable in its result type.

The code changes are in this PR: https://github.com/jasonbobier/swift-numerics/pull/1

It currently is waiting on the resolution of https://github.com/apple/swift-numerics/pull/320 and then the base will be switched to apple/numerics.

Start by reviewing jasonbobier/swift-numerics#1 and the pending dependency apple/swift-numerics#320, since the proposed implementation is already there and is waiting on that resolution. Done means the least-common-multiple API is integrated after the base changes, with both overflow behaviors covered by the package's tests.

Written by the indexing model from the issue text.