CombineLatest for an array of upstreams

I have a need for an algorithm that's like the existing CombineLatest, but for an array of upstream async sequences that all share the same element type.

The number of upstream is not known at build time, so this isn't an ask for CombineLatest with variadic generics.

Start by reading the existing CombineLatest implementation and the open pull request #360, which appears to address this request. Confirm the intended behavior for an array whose size is only known at runtime, then identify the relevant test coverage and ensure the requested array-based algorithm is exercised before considering the issue done.

Written by the indexing model from the issue text.