“Lazy Map” capability for the BQSKit runtime

[WolfLink]

I’d like the ability to perform a “lazy map”, meaning to have a RuntimeFuture to which I can submit more tasks. Here’s an example scenario where this would be useful:

1. I start an asynchronous task A
2. I perform some other code
3. I start an asynchronous task B
4. I wait for a result from either A or B (whichever finishes first)
5. I cancel the other task (or all such other tasks if you expand this pattern beyond 2 tasks).

I imagine the code looking something like this:

lazy_map = get_runtime().lazy_map()
lazy_map.submit(A)
# other code
lazy_map.submit(B)
result = await lazy_map
lazy_map.cancel()

Another way to do this would be a way to await a list of futures