Try "2-sided" communication for payloads

[everythingfunctional]

I had the thought that co_broadcast is supposed to support polymorphism (components at least). Also, there's a point at which the scheduler and executor are somewhat "synchronizing". We could implement a send/receive operation using teams and co_broadcast. I.e. the two images involved create and join a team, and then call co_broadcast. This would allow us to support polymorphic payloads, and users wouldn't have to manually (de)serialize their data.

[everythingfunctional]

This would require the tasks to send their result back to the scheduler as well.

[everythingfunctional]

And I just noticed that form team is a collective operation. So you can't on the fly form a team between two images and have them join it (I don't understand why this is, but ok). So we'd have to construct the set of teams we need before we start running the tasks.