Possible race condition in PPE-enabled `Actor.pushData`

[janbuchar]

          FYI: By moving the push before the charge, we introduced a small race condition where as we are close to the max budget, more pushes can happen concurrently and we could push a few more items than we can charge for. I think this might happen maybe in 1/1000 runs, maybe even less (depends on the size of the data push which determines the latency of it).

I thought a bit about fixes for this and haven't come up with anything elegant. You could have a new bookFutureCharge method to pre-register events but it would introduce a new complex API. Or we could patch it on the Actor class bypassing the manager and just handle in the pushData. All of it introduces extra complexities. So for now I'm parking that thought because I don't think it is a big deal.

Originally posted by @metalwarrior665 in #346 (comment)