Add specific fiber tests across multiple threads

[mdsitton]

I was looking over the fiber tests and i noticed they were all single threaded. https://github.com/RichieSams/FiberTaskingLib/tree/master/tests/fiber_abstraction

Catch2 has some limitations for access from multiple threads so it would need to be carefully done: https://github.com/catchorg/Catch2/blob/devel/docs/limitations.md

But i think this could help ensure there aren't issues at this level when migrating fibers across threads and whatnot.

edit: Clarification that i mean for just the fiber abstraction tests, i know that there are other tests for the other parts of the library that may eventually trigger thread usage.