Feature: Allow for concurrent processing of call blocks

[pault-t-canva]

Rather than have to spawn out multiple sessions it'd be nice if someone could have a way to have calls run at the same time.

I'm thinking this should probably take place by providing ordering on a call, where by default each subsequent call would be +1 the prior one. That would mean you could do something like

runHttp {
   call() {
     order = 1
   }
   call {
     order = 2
   } 
   call {
     order = 2
   }
}

and in the above all calls from 1 finish prior to 2 starting. calls from 2 are likely to intermix.

The challenge here is that other calls might pipe to each other so it'll be interesting to see how it figures out if the call is done. Likely just an empty channel from all of them at the same time.